// Copyright 2021 DeepMind Technologies Limited
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "xml/xml_native_reader.h"

#include <array>
#include <cstddef>
#include <cstdio>
#include <cstring>
#include <functional>
#include <limits>
#include <map>
#include <optional>
#include <sstream>
#include <string>
#include <string_view>
#include <utility>
#include <vector>

#include "tinyxml2.h"

#include <mujoco/mujoco.h>
#include <mujoco/mjmodel.h>
#include <mujoco/mjplugin.h>
#include <mujoco/mjtnum.h>
#include <mujoco/mjvisualize.h>
#include "engine/engine_plugin.h"
#include "engine/engine_util_errmem.h"
#include "engine/engine_util_misc.h"
#include <mujoco/mjspec.h>
#include "user/user_api.h"
#include "user/user_composite.h"
#include "user/user_flexcomp.h"
#include "user/user_util.h"
#include "xml/xml_base.h"
#include "xml/xml_util.h"

namespace {
using std::string;
using std::string_view;
using std::vector;
using mujoco::user::FilePath;
using tinyxml2::XMLElement;

void ReadPluginConfigs(tinyxml2::XMLElement* elem, mjsPlugin* p) {
  std::map<string, string, std::less<>> config_attribs;
  XMLElement* child = FirstChildElement(elem);
  while (child) {
    string_view name = child->Value();
    if (name == "config") {
      string key, value;
      mjXUtil::ReadAttrTxt(child, "key", key, /* required = */ true);
      if (config_attribs.find(key) != config_attribs.end()) {
        string err = "duplicate config key: " + key;
        throw mjXError(child, "%s", err.c_str());
      }
      mjXUtil::ReadAttrTxt(child, "value", value, /* required = */ true);
      config_attribs[key] = value;
    }
    child = NextSiblingElement(child);
  }

  if (!p && !config_attribs.empty()) {
    throw mjXError(elem,
                   "plugin configuration attributes cannot be used in an "
                   "element that references a predefined plugin instance");
  } else if (p) {
    mjs_setPluginAttributes(p, &config_attribs);
  }
}

static void UpdateString(string& psuffix, int count, int i) {
  int ndigits = std::to_string(count).length();
  string i_string = std::to_string(i);
  string prefix = "";
  while (ndigits-- > i_string.length()) {
    prefix += '0';
  }
  psuffix += prefix + i_string;
}
}  // namespace


//---------------------------------- MJCF schema ---------------------------------------------------

const char* MJCF[nMJCF][mjXATTRNUM] = {
{"mujoco", "!", "1", "model"},
{"<"},
    {"compiler", "*", "20", "autolimits", "boundmass", "boundinertia", "settotalmass",
        "balanceinertia", "strippath", "coordinate", "angle", "fitaabb", "eulerseq",
        "meshdir", "texturedir", "discardvisual", "convexhull", "usethread",
        "fusestatic", "inertiafromgeom", "inertiagrouprange", "exactmeshinertia",
        "assetdir"},
    {"<"},
        {"lengthrange", "?", "10", "mode", "useexisting", "uselimit",
            "accel", "maxforce", "timeconst", "timestep",
            "inttotal", "interval", "tolrange"},
    {">"},

    {"option", "*", "27",
        "timestep", "apirate", "impratio", "tolerance", "ls_tolerance", "noslip_tolerance",
        "mpr_tolerance", "gravity", "wind", "magnetic", "density", "viscosity",
        "o_margin", "o_solref", "o_solimp", "o_friction",
        "integrator", "cone", "jacobian",
        "solver", "iterations", "ls_iterations", "noslip_iterations", "mpr_iterations",
        "sdf_iterations", "sdf_initpoints", "actuatorgroupdisable"},
    {"<"},
        {"flag", "?", "22", "constraint", "equality", "frictionloss", "limit", "contact",
            "passive", "gravity", "clampctrl", "warmstart",
            "filterparent", "actuation", "refsafe", "sensor", "midphase", "eulerdamp", "autoreset",
            "override", "energy", "fwdinv", "invdiscrete", "multiccd", "island"},
    {">"},

    {"size", "*", "14", "memory", "njmax", "nconmax", "nstack", "nuserdata", "nkey",
        "nuser_body", "nuser_jnt", "nuser_geom", "nuser_site", "nuser_cam",
        "nuser_tendon", "nuser_actuator", "nuser_sensor"},

    {"visual", "*", "0"},
    {"<"},
        {"global", "?", "12", "orthographic", "fovy", "ipd", "azimuth", "elevation", "linewidth",
            "glow", "offwidth", "offheight", "realtime", "ellipsoidinertia", "bvactive"},
        {"quality", "?", "5", "shadowsize", "offsamples", "numslices", "numstacks",
            "numquads"},
        {"headlight", "?", "4", "ambient", "diffuse", "specular", "active"},
        {"map", "?", "13", "stiffness", "stiffnessrot", "force", "torque", "alpha",
            "fogstart", "fogend", "znear", "zfar", "haze", "shadowclip", "shadowscale",
            "actuatortendon"},
        {"scale", "?", "17", "forcewidth", "contactwidth", "contactheight", "connect", "com",
            "camera", "light", "selectpoint", "jointlength", "jointwidth", "actuatorlength",
            "actuatorwidth", "framelength", "framewidth", "constraint", "slidercrank", "frustum"},
        {"rgba", "?", "25", "fog", "haze", "force", "inertia", "joint",
            "actuator", "actuatornegative", "actuatorpositive", "com",
            "camera", "light", "selectpoint", "connect", "contactpoint", "contactforce",
            "contactfriction", "contacttorque", "contactgap", "rangefinder",
            "constraint", "slidercrank", "crankbroken", "frustum", "bv", "bvactive"},
    {">"},

    {"statistic", "*", "5", "meaninertia", "meanmass", "meansize", "extent", "center"},

    {"default", "R", "1", "class"},
    {"<"},
        {"mesh", "?", "2", "scale", "maxhullvert"},
        {"material", "?", "10", "texture", "emission", "specular", "shininess",
            "reflectance", "metallic", "roughness", "rgba", "texrepeat", "texuniform"},
        {"joint", "?", "22", "type", "group", "pos", "axis", "springdamper",
            "limited", "actuatorfrclimited", "solreflimit", "solimplimit",
            "solreffriction", "solimpfriction", "stiffness", "range", "actuatorfrcrange",
            "actuatorgravcomp", "margin", "ref", "springref", "armature", "damping",
            "frictionloss", "user"},
        {"geom", "?", "31", "type", "pos", "quat", "contype", "conaffinity", "condim",
            "group", "priority", "size", "material", "friction", "mass", "density",
            "shellinertia", "solmix", "solref", "solimp",
            "margin", "gap", "fromto", "axisangle", "xyaxes", "zaxis", "euler",
            "hfield", "mesh", "fitscale", "rgba", "fluidshape", "fluidcoef", "user"},
        {"site", "?", "13", "type", "group", "pos", "quat", "material",
            "size", "fromto", "axisangle", "xyaxes", "zaxis", "euler", "rgba", "user"},
        {"camera", "?", "17", "orthographic", "fovy", "ipd", "resolution", "pos", "quat",
            "axisangle", "xyaxes", "zaxis", "euler", "mode", "focal", "focalpixel",
            "principal", "principalpixel", "sensorsize", "user"},
        {"light", "?", "13", "pos", "dir", "bulbradius", "directional", "castshadow", "active",
            "attenuation", "cutoff", "exponent", "ambient", "diffuse", "specular", "mode"},
        {"pair", "?", "7", "condim", "friction", "solref", "solreffriction", "solimp",
         "gap", "margin"},
        {"equality", "?", "3", "active", "solref", "solimp"},
        {"tendon", "?", "16", "group", "limited", "range",
            "solreflimit", "solimplimit", "solreffriction", "solimpfriction",
            "frictionloss", "springlength", "width", "material",
            "margin", "stiffness", "damping", "rgba", "user"},
        {"general", "?", "18", "ctrllimited", "forcelimited", "actlimited", "ctrlrange",
            "forcerange", "actrange", "gear", "cranklength", "user", "group", "actdim",
            "dyntype", "gaintype", "biastype", "dynprm", "gainprm", "biasprm", "actearly"},
        {"motor", "?", "8", "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
            "gear", "cranklength", "user", "group"},
        {"position", "?", "13", "ctrllimited", "forcelimited", "ctrlrange", "inheritrange",
            "forcerange", "gear", "cranklength", "user", "group", "kp", "kv", "dampratio", "timeconst"},
        {"velocity", "?", "9", "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
            "gear", "cranklength", "user", "group", "kv"},
        {"intvelocity", "?", "13", "ctrllimited", "forcelimited",
            "ctrlrange", "forcerange", "actrange", "inheritrange",
            "gear", "cranklength", "user", "group",
            "kp", "kv", "dampratio"},
        {"damper", "?", "8", "forcelimited", "ctrlrange", "forcerange",
            "gear", "cranklength", "user", "group", "kv"},
        {"cylinder", "?", "12", "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
            "gear", "cranklength", "user", "group",
            "timeconst", "area", "diameter", "bias"},
        {"muscle", "?", "17", "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
            "gear", "cranklength", "user", "group",
            "timeconst", "range", "force", "scale",
            "lmin", "lmax", "vmax", "fpmax", "fvmax"},
        {"adhesion", "?", "6", "forcelimited", "ctrlrange", "forcerange",
            "gain", "user", "group"},
    {">"},

    {"extension", "*", "0"},
    {"<"},
        {"plugin", "*", "1", "plugin"},
        {"<"},
            {"instance", "*", "1", "name"},
            {"<"},
                {"config", "*", "2", "key", "value"},
            {">"},
        {">"},
    {">"},

    {"custom", "*", "0"},
    {"<"},
        {"numeric", "*", "3", "name", "size", "data"},
        {"text", "*", "2", "name", "data"},
        {"tuple", "*", "1", "name"},
        {"<"},
            {"element", "*", "3", "objtype", "objname", "prm"},
        {">"},
    {">"},

    {"asset", "*", "0"},
    {"<"},
        {"mesh", "*", "13", "name", "class", "content_type", "file", "vertex", "normal",
            "texcoord", "face", "refpos", "refquat", "scale", "smoothnormal",
            "maxhullvert"},
        {"<"},
          {"plugin", "*", "2", "plugin", "instance"},
          {"<"},
            {"config", "*", "2", "key", "value"},
          {">"},
        {">"},
        {"hfield", "*", "7", "name", "content_type", "file", "nrow", "ncol", "size", "elevation"},
        {"skin", "*", "9", "name", "file", "material", "rgba", "inflate",
            "vertex", "texcoord", "face", "group"},
        {"<"},
            {"bone", "*", "5", "body", "bindpos", "bindquat", "vertid", "vertweight"},
        {">"},
        {"texture", "*", "23", "name", "type", "content_type", "file", "gridsize", "gridlayout",
            "fileright", "fileleft", "fileup", "filedown", "filefront", "fileback",
            "builtin", "rgb1", "rgb2", "mark", "markrgb", "random", "width", "height",
            "hflip", "vflip", "nchannel"},
        {"material", "*", "12", "name", "class", "texture",  "texrepeat", "texuniform",
            "emission", "specular", "shininess", "reflectance", "metallic", "roughness", "rgba"},
        {"<"},
            {"rgb", "?", "1", "texture"},
            {"occlusion", "?", "1", "texture"},
            {"roughness", "?", "1", "texture"},
            {"metallic", "?", "1", "texture"},
            {"normal", "?", "1", "texture"},
            {"opacity", "?", "1", "texture"},
            {"emissive", "?", "1", "texture"},
            {"rgba", "?", "1", "texture"},
            {"orm", "?", "1", "texture"},
        {">"},
        {"model", "*", "2", "name", "file"},
    {">"},

    {"body", "R", "11", "name", "childclass", "pos", "quat", "mocap",
        "axisangle", "xyaxes", "zaxis", "euler", "gravcomp", "user"},
    {"<"},
        {"inertial", "?", "9", "pos", "quat", "mass", "diaginertia",
            "axisangle", "xyaxes", "zaxis", "euler", "fullinertia"},
        {"joint", "*", "24", "name", "class", "type", "group", "pos", "axis",
            "springdamper", "limited", "actuatorfrclimited",
            "solreflimit", "solimplimit", "solreffriction", "solimpfriction",
            "stiffness", "range", "actuatorfrcrange", "actuatorgravcomp", "margin", "ref",
            "springref", "armature", "damping", "frictionloss", "user"},
        {"freejoint", "*", "2", "name", "group"},
        {"geom", "*", "33", "name", "class", "type", "contype", "conaffinity", "condim",
            "group", "priority", "size", "material", "friction", "mass", "density",
            "shellinertia", "solmix", "solref", "solimp",
            "margin", "gap", "fromto", "pos", "quat", "axisangle", "xyaxes", "zaxis", "euler",
            "hfield", "mesh", "fitscale", "rgba", "fluidshape", "fluidcoef", "user"},
        {"<"},
            {"plugin", "*", "2", "plugin", "instance"},
            {"<"},
              {"config", "*", "2", "key", "value"},
            {">"},
        {">"},
        {"attach", "*", "3", "model", "body", "prefix"},
        {"site", "*", "15", "name", "class", "type", "group", "pos", "quat",
            "material", "size", "fromto", "axisangle", "xyaxes", "zaxis", "euler", "rgba", "user"},
        {"camera", "*", "20", "name", "class", "orthographic", "fovy", "ipd", "resolution", "pos",
            "quat", "axisangle", "xyaxes", "zaxis", "euler", "mode", "target",
            "focal", "focalpixel", "principal", "principalpixel", "sensorsize", "user"},
        {"light", "*", "16", "name", "class", "directional", "castshadow", "active",
            "pos", "dir", "bulbradius", "attenuation", "cutoff", "exponent", "ambient", "diffuse",
            "specular", "mode", "target"},
        {"plugin", "*", "2", "plugin", "instance"},
        {"<"},
          {"config", "*", "2", "key", "value"},
        {">"},
        {"composite", "*", "13", "prefix", "type", "count", "spacing", "offset",
            "flatinertia", "solrefsmooth", "solimpsmooth", "vertex", "face",
            "initial", "curve", "size"},
        {"<"},
            {"joint", "*", "17", "kind", "group", "stiffness", "damping", "armature",
                "solreffix", "solimpfix", "type", "axis",
                "limited", "range", "margin", "solreflimit", "solimplimit",
                "frictionloss", "solreffriction", "solimpfriction"},
            {"tendon", "*", "17", "kind", "group", "stiffness", "damping",
                "solreffix", "solimpfix",
                "limited", "range", "margin", "solreflimit", "solimplimit",
                "frictionloss", "solreffriction", "solimpfriction",
                "material", "rgba", "width"},
            {"skin", "?", "6", "texcoord", "material", "group", "rgba", "inflate", "subgrid"},
            {"geom", "?", "17", "type", "contype", "conaffinity", "condim",
                "group", "priority", "size", "material", "rgba", "friction", "mass",
                "density", "solmix", "solref", "solimp", "margin", "gap"},
            {"site", "?", "4", "group", "size", "material", "rgba"},
            {"pin", "*", "1", "coord"},
            {"plugin", "*", "2", "plugin", "instance"},
            {"<"},
              {"config", "*", "2", "key", "value"},
            {">"},
        {">"},
        {"flexcomp", "*", "24", "name", "type", "group", "dim",
            "count", "spacing", "radius", "rigid", "mass", "inertiabox",
            "scale", "file", "point", "element", "texcoord", "material", "rgba",
            "flatskin", "pos", "quat", "axisangle", "xyaxes", "zaxis", "euler"},
        {"<"},
            {"edge", "?", "5", "equality", "solref", "solimp", "stiffness", "damping"},
            {"contact", "?", "13", "contype", "conaffinity", "condim", "priority",
                "friction", "solmix", "solref", "solimp", "margin", "gap",
                "internal", "selfcollide", "activelayers"},
            {"pin", "*", "4", "id", "range", "grid", "gridrange"},
            {"plugin", "*", "2", "plugin", "instance"},
            {"<"},
              {"config", "*", "2", "key", "value"},
            {">"},
        {">"},
    {">"},

    {"deformable", "*", "0"},
    {"<"},
        {"flex", "*", "11", "name", "group", "dim", "radius", "material",
            "rgba", "flatskin", "body", "vertex", "element", "texcoord"},
        {"<"},
            {"contact", "?", "13", "contype", "conaffinity", "condim", "priority",
                "friction", "solmix", "solref", "solimp", "margin", "gap",
                "internal", "selfcollide", "activelayers"},
            {"edge", "?", "2", "stiffness", "damping"},
        {">"},
        {"skin", "*", "9", "name", "file", "material", "rgba", "inflate",
            "vertex", "texcoord", "face", "group"},
        {"<"},
            {"bone", "*", "5", "body", "bindpos", "bindquat", "vertid", "vertweight"},
        {">"},
    {">"},

    {"contact", "*", "0"},
    {"<"},
        {"pair", "*", "11", "name", "class", "geom1", "geom2", "condim", "friction",
            "solref", "solreffriction", "solimp", "gap", "margin"},
        {"exclude", "*", "3", "name", "body1", "body2"},
    {">"},

    {"equality", "*", "0"},
    {"<"},
        {"connect", "*", "8", "name", "class", "body1", "body2", "anchor",
            "active", "solref", "solimp"},
        {"weld", "*", "10", "name", "class", "body1", "body2", "relpose", "anchor",
            "active", "solref", "solimp", "torquescale"},
        {"joint", "*", "8", "name", "class", "joint1", "joint2", "polycoef",
            "active", "solref", "solimp"},
        {"tendon", "*", "8", "name", "class", "tendon1", "tendon2", "polycoef",
            "active", "solref", "solimp"},
        {"flex", "*", "6", "name", "class", "flex",
            "active", "solref", "solimp"},
    {">"},

    {"tendon", "*", "0"},
    {"<"},
        {"spatial", "*", "18", "name", "class", "group", "limited", "range",
            "solreflimit", "solimplimit", "solreffriction", "solimpfriction",
            "frictionloss", "springlength", "width", "material",
            "margin", "stiffness", "damping", "rgba", "user"},
        {"<"},
            {"site", "*", "1", "site"},
            {"geom", "*", "2", "geom", "sidesite"},
            {"pulley", "*", "1", "divisor"},
        {">"},
        {"fixed", "*", "15", "name", "class", "group", "limited", "range",
            "solreflimit", "solimplimit", "solreffriction", "solimpfriction",
            "frictionloss", "springlength", "margin", "stiffness", "damping", "user"},
        {"<"},
            {"joint", "*", "2", "joint", "coef"},
        {">"},
    {">"},

    {"actuator", "*", "0"},
    {"<"},
        {"general", "*", "29", "name", "class", "group",
            "ctrllimited", "forcelimited", "actlimited", "ctrlrange", "forcerange", "actrange",
            "lengthrange", "gear", "cranklength", "user",
            "joint", "jointinparent", "tendon", "slidersite", "cranksite", "site", "refsite",
            "body", "actdim", "dyntype", "gaintype", "biastype", "dynprm", "gainprm", "biasprm",
            "actearly"},
        {"motor", "*", "18", "name", "class", "group",
            "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
            "lengthrange", "gear", "cranklength", "user",
            "joint", "jointinparent", "tendon", "slidersite", "cranksite", "site", "refsite"},
        {"position", "*", "23", "name", "class", "group",
            "ctrllimited", "forcelimited", "ctrlrange", "inheritrange", "forcerange",
            "lengthrange", "gear", "cranklength", "user",
            "joint", "jointinparent", "tendon", "slidersite", "cranksite", "site", "refsite",
            "kp", "kv", "dampratio", "timeconst"},
        {"velocity", "*", "19", "name", "class", "group",
            "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
            "lengthrange", "gear", "cranklength", "user",
            "joint", "jointinparent", "tendon", "slidersite", "cranksite", "site", "refsite",
            "kv"},
        {"intvelocity", "*", "23", "name", "class", "group",
            "ctrllimited", "forcelimited",
            "ctrlrange", "forcerange", "actrange", "inheritrange", "lengthrange",
            "gear", "cranklength", "user",
            "joint", "jointinparent", "tendon", "slidersite", "cranksite", "site", "refsite",
            "kp", "kv", "dampratio"},
        {"damper", "*", "18", "name", "class", "group",
            "forcelimited", "ctrlrange", "forcerange",
            "lengthrange", "gear", "cranklength", "user",
            "joint", "jointinparent", "tendon", "slidersite", "cranksite", "site", "refsite",
            "kv"},
        {"cylinder", "*", "22", "name", "class", "group",
            "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
            "lengthrange", "gear", "cranklength", "user",
            "joint", "jointinparent", "tendon", "slidersite", "cranksite", "site", "refsite",
            "timeconst", "area", "diameter", "bias"},
        {"muscle", "*", "26",  "name", "class", "group",
            "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
            "lengthrange", "gear", "cranklength", "user",
            "joint", "jointinparent", "tendon", "slidersite", "cranksite",
            "timeconst", "tausmooth", "range", "force", "scale",
            "lmin", "lmax", "vmax", "fpmax", "fvmax"},
        {"adhesion", "*", "9", "name", "class", "group",
            "forcelimited", "ctrlrange", "forcerange", "user", "body", "gain"},
        {"plugin", "*", "25", "name", "class",  "plugin", "instance", "group",
            "ctrllimited", "forcelimited", "actlimited", "ctrlrange", "forcerange", "actrange",
            "lengthrange", "gear", "cranklength", "joint", "jointinparent",
            "site", "actdim", "dyntype", "dynprm", "tendon", "cranksite", "slidersite", "user",
            "actearly"},
        {"<"},
          {"config", "*", "2", "key", "value"},
        {">"},
    {">"},

    {"sensor", "*", "0"},
    {"<"},
        {"touch", "*", "5", "name", "site", "cutoff", "noise", "user"},
        {"accelerometer", "*", "5", "name", "site", "cutoff", "noise", "user"},
        {"velocimeter", "*", "5", "name", "site", "cutoff", "noise", "user"},
        {"gyro", "*", "5", "name", "site", "cutoff", "noise", "user"},
        {"force", "*", "5", "name", "site", "cutoff", "noise", "user"},
        {"torque", "*", "5", "name", "site", "cutoff", "noise", "user"},
        {"magnetometer", "*", "5", "name", "site", "cutoff", "noise", "user"},
        {"camprojection", "*", "6", "name", "site", "camera", "cutoff", "noise", "user"},
        {"rangefinder", "*", "5", "name", "site", "cutoff", "noise", "user"},
        {"jointpos", "*", "5", "name", "joint", "cutoff", "noise", "user"},
        {"jointvel", "*", "5", "name", "joint", "cutoff", "noise", "user"},
        {"tendonpos", "*", "5", "name", "tendon", "cutoff", "noise", "user"},
        {"tendonvel", "*", "5", "name", "tendon", "cutoff", "noise", "user"},
        {"actuatorpos", "*", "5", "name", "actuator", "cutoff", "noise", "user"},
        {"actuatorvel", "*", "5", "name", "actuator", "cutoff", "noise", "user"},
        {"actuatorfrc", "*", "5", "name", "actuator", "cutoff", "noise", "user"},
        {"jointactuatorfrc", "*", "5", "name", "joint", "cutoff", "noise", "user"},
        {"ballquat", "*", "5", "name", "joint", "cutoff", "noise", "user"},
        {"ballangvel", "*", "5", "name", "joint", "cutoff", "noise", "user"},
        {"jointlimitpos", "*", "5", "name", "joint", "cutoff", "noise", "user"},
        {"jointlimitvel", "*", "5", "name", "joint", "cutoff", "noise", "user"},
        {"jointlimitfrc", "*", "5", "name", "joint", "cutoff", "noise", "user"},
        {"tendonlimitpos", "*", "5", "name", "tendon", "cutoff", "noise", "user"},
        {"tendonlimitvel", "*", "5", "name", "tendon", "cutoff", "noise", "user"},
        {"tendonlimitfrc", "*", "5", "name", "tendon", "cutoff", "noise", "user"},
        {"framepos", "*", "8", "name", "objtype", "objname", "reftype", "refname", "cutoff", "noise", "user"},
        {"framequat", "*", "8", "name", "objtype", "objname", "reftype", "refname", "cutoff", "noise", "user"},
        {"framexaxis", "*", "8", "name", "objtype", "objname", "reftype", "refname", "cutoff", "noise", "user"},
        {"frameyaxis", "*", "8", "name", "objtype", "objname", "reftype", "refname", "cutoff", "noise", "user"},
        {"framezaxis", "*", "8", "name", "objtype", "objname", "reftype", "refname", "cutoff", "noise", "user"},
        {"framelinvel", "*", "8", "name", "objtype", "objname", "reftype", "refname", "cutoff", "noise", "user"},
        {"frameangvel", "*", "8", "name", "objtype", "objname", "reftype", "refname", "cutoff", "noise", "user"},
        {"framelinacc", "*", "6", "name", "objtype", "objname", "cutoff", "noise", "user"},
        {"frameangacc", "*", "6", "name", "objtype", "objname", "cutoff", "noise", "user"},
        {"subtreecom", "*", "5", "name", "body", "cutoff", "noise", "user"},
        {"subtreelinvel", "*", "5", "name", "body", "cutoff", "noise", "user"},
        {"subtreeangmom", "*", "5", "name", "body", "cutoff", "noise", "user"},
        {"distance", "*", "8", "name", "geom1", "geom2", "body1", "body2", "cutoff", "noise", "user"},
        {"normal", "*", "8", "name", "geom1", "geom2", "body1", "body2", "cutoff", "noise", "user"},
        {"fromto", "*", "8", "name", "geom1", "geom2", "body1", "body2", "cutoff", "noise", "user"},
        {"clock", "*", "4", "name", "cutoff", "noise", "user"},
        {"user", "*", "9", "name", "objtype", "objname", "datatype", "needstage",
            "dim", "cutoff", "noise", "user"},
        {"plugin", "*", "9", "name", "plugin", "instance", "cutoff", "objtype", "objname", "reftype", "refname",
            "user"},
        {"<"},
          {"config", "*", "2", "key", "value"},
        {">"},
    {">"},

    {"keyframe", "*", "0"},
    {"<"},
        {"key", "*", "8", "name", "time", "qpos", "qvel", "act", "mpos", "mquat", "ctrl"},
    {">"},
{">"}
};



//---------------------------------- MJCF keywords used in attributes ------------------------------

// coordinate type
const mjMap coordinate_map[2] = {
  {"local",   0},
  {"global",  1}
};


// angle type
const mjMap angle_map[2] = {
  {"radian",  0},
  {"degree",  1}
};


// bool type
const mjMap bool_map[2] = {
  {"false",   0},
  {"true",    1}
};


// fluidshape type
const mjMap fluid_map[2] = {
  {"none",      0},
  {"ellipsoid", 1}
};


// enable type
const mjMap enable_map[2] = {
  {"disable", 0},
  {"enable",  1}
};


// TFAuto type
const mjMap TFAuto_map[3] = {
  {"false",   0},
  {"true",    1},
  {"auto",    2}
};


// joint type
const int joint_sz = 4;
const mjMap joint_map[joint_sz] = {
  {"free",        mjJNT_FREE},
  {"ball",        mjJNT_BALL},
  {"slide",       mjJNT_SLIDE},
  {"hinge",       mjJNT_HINGE}
};


// geom type
const mjMap geom_map[mjNGEOMTYPES] = {
  {"plane",       mjGEOM_PLANE},
  {"hfield",      mjGEOM_HFIELD},
  {"sphere",      mjGEOM_SPHERE},
  {"capsule",     mjGEOM_CAPSULE},
  {"ellipsoid",   mjGEOM_ELLIPSOID},
  {"cylinder",    mjGEOM_CYLINDER},
  {"box",         mjGEOM_BOX},
  {"mesh",        mjGEOM_MESH},
  {"sdf",         mjGEOM_SDF}
};


// camlight type
const int camlight_sz = 5;
const mjMap camlight_map[camlight_sz] = {
  {"fixed",         mjCAMLIGHT_FIXED},
  {"track",         mjCAMLIGHT_TRACK},
  {"trackcom",      mjCAMLIGHT_TRACKCOM},
  {"targetbody",    mjCAMLIGHT_TARGETBODY},
  {"targetbodycom", mjCAMLIGHT_TARGETBODYCOM}
};

// texmat role type
const int texrole_sz = mjNTEXROLE - 1;
const mjMap texrole_map[texrole_sz] = {
  {"rgb",           mjTEXROLE_RGB},
  {"occlusion",     mjTEXROLE_OCCLUSION},
  {"roughness",     mjTEXROLE_ROUGHNESS},
  {"metallic",      mjTEXROLE_METALLIC},
  {"normal",        mjTEXROLE_NORMAL},
  {"opacity",       mjTEXROLE_OPACITY},
  {"emissive",      mjTEXROLE_EMISSIVE},
  {"rgba",          mjTEXROLE_RGBA},
  {"orm",           mjTEXROLE_ORM},
};

// integrator type
const int integrator_sz = 4;
const mjMap integrator_map[integrator_sz] = {
  {"Euler",        mjINT_EULER},
  {"RK4",          mjINT_RK4},
  {"implicit",     mjINT_IMPLICIT},
  {"implicitfast", mjINT_IMPLICITFAST}
};

// cone type
const int cone_sz = 2;
const mjMap cone_map[cone_sz] = {
  {"pyramidal",   mjCONE_PYRAMIDAL},
  {"elliptic",    mjCONE_ELLIPTIC}
};


// Jacobian type
const int jac_sz = 3;
const mjMap jac_map[jac_sz] = {
  {"dense",       mjJAC_DENSE},
  {"sparse",      mjJAC_SPARSE},
  {"auto",        mjJAC_AUTO}
};


// solver type
const int solver_sz = 3;
const mjMap solver_map[solver_sz] = {
  {"PGS",         mjSOL_PGS},
  {"CG",          mjSOL_CG},
  {"Newton",      mjSOL_NEWTON}
};


// constraint type
const int equality_sz = 6;
const mjMap equality_map[equality_sz] = {
  {"connect",     mjEQ_CONNECT},
  {"weld",        mjEQ_WELD},
  {"joint",       mjEQ_JOINT},
  {"tendon",      mjEQ_TENDON},
  {"flex",        mjEQ_FLEX},
  {"distance",    mjEQ_DISTANCE}
};


// type for texture
const int texture_sz = 3;
const mjMap texture_map[texture_sz] = {
  {"2d",          mjTEXTURE_2D},
  {"cube",        mjTEXTURE_CUBE},
  {"skybox",      mjTEXTURE_SKYBOX}
};


// builtin type for texture
const int builtin_sz = 4;
const mjMap builtin_map[builtin_sz] = {
  {"none",        mjBUILTIN_NONE},
  {"gradient",    mjBUILTIN_GRADIENT},
  {"checker",     mjBUILTIN_CHECKER},
  {"flat",        mjBUILTIN_FLAT}
};


// mark type for texture
const int mark_sz = 4;
const mjMap mark_map[mark_sz] = {
  {"none",        mjMARK_NONE},
  {"edge",        mjMARK_EDGE},
  {"cross",       mjMARK_CROSS},
  {"random",      mjMARK_RANDOM}
};


// dyn type
const int dyn_sz = 6;
const mjMap dyn_map[dyn_sz] = {
  {"none",        mjDYN_NONE},
  {"integrator",  mjDYN_INTEGRATOR},
  {"filter",      mjDYN_FILTER},
  {"filterexact", mjDYN_FILTEREXACT},
  {"muscle",      mjDYN_MUSCLE},
  {"user",        mjDYN_USER}
};


// gain type
const int gain_sz = 4;
const mjMap gain_map[gain_sz] = {
  {"fixed",       mjGAIN_FIXED},
  {"affine",      mjGAIN_AFFINE},
  {"muscle",      mjGAIN_MUSCLE},
  {"user",        mjGAIN_USER}
};


// bias type
const int bias_sz = 4;
const mjMap bias_map[bias_sz] = {
  {"none",        mjBIAS_NONE},
  {"affine",      mjBIAS_AFFINE},
  {"muscle",      mjBIAS_MUSCLE},
  {"user",        mjBIAS_USER}
};


// stage type
const int stage_sz = 4;
const mjMap stage_map[stage_sz] = {
  {"none",        mjSTAGE_NONE},
  {"pos",         mjSTAGE_POS},
  {"vel",         mjSTAGE_VEL},
  {"acc",         mjSTAGE_ACC}
};


// data type
const int datatype_sz = 4;
const mjMap datatype_map[datatype_sz] = {
  {"real",        mjDATATYPE_REAL},
  {"positive",    mjDATATYPE_POSITIVE},
  {"axis",        mjDATATYPE_AXIS},
  {"quaternion",  mjDATATYPE_QUATERNION}
};


// LR mode
const int lrmode_sz = 4;
const mjMap lrmode_map[lrmode_sz] = {
  {"none",        mjLRMODE_NONE},
  {"muscle",      mjLRMODE_MUSCLE},
  {"muscleuser",  mjLRMODE_MUSCLEUSER},
  {"all",         mjLRMODE_ALL}
};


// composite type
const mjMap comp_map[mjNCOMPTYPES] = {
  {"particle",    mjCOMPTYPE_PARTICLE},
  {"grid",        mjCOMPTYPE_GRID},
  {"rope",        mjCOMPTYPE_ROPE},
  {"loop",        mjCOMPTYPE_LOOP},
  {"cable",       mjCOMPTYPE_CABLE},
  {"cloth",       mjCOMPTYPE_CLOTH},
  {"box",         mjCOMPTYPE_BOX},
  {"cylinder",    mjCOMPTYPE_CYLINDER},
  {"ellipsoid",   mjCOMPTYPE_ELLIPSOID}
};


// composite joint kind
const mjMap jkind_map[4] = {
  {"main",        mjCOMPKIND_JOINT},
  {"twist",       mjCOMPKIND_TWIST},
  {"stretch",     mjCOMPKIND_STRETCH},
  {"particle",    mjCOMPKIND_PARTICLE}
};


// composite rope shape
const mjMap shape_map[mjNCOMPSHAPES] = {
  {"s",           mjCOMPSHAPE_LINE},
  {"cos(s)",      mjCOMPSHAPE_COS},
  {"sin(s)",      mjCOMPSHAPE_SIN},
  {"0",           mjCOMPSHAPE_ZERO}
};


// composite tendon kind
const mjMap tkind_map[2] = {
  {"main",        mjCOMPKIND_TENDON},
  {"shear",       mjCOMPKIND_SHEAR}
};


// mesh type
const mjMap meshtype_map[2] = {
  {"false", mjINERTIA_VOLUME},
  {"true",  mjINERTIA_SHELL},
};


// flexcomp type
const mjMap fcomp_map[mjNFCOMPTYPES] = {
  {"grid",        mjFCOMPTYPE_GRID},
  {"box",         mjFCOMPTYPE_BOX},
  {"cylinder",    mjFCOMPTYPE_CYLINDER},
  {"ellipsoid",   mjFCOMPTYPE_ELLIPSOID},
  {"square",      mjFCOMPTYPE_SQUARE},
  {"disc",        mjFCOMPTYPE_DISC},
  {"mesh",        mjFCOMPTYPE_MESH},
  {"gmsh",        mjFCOMPTYPE_GMSH},
  {"direct",      mjFCOMPTYPE_DIRECT}
};


// flex selfcollide type
const mjMap flexself_map[5] = {
  {"none",        mjFLEXSELF_NONE},
  {"narrow",      mjFLEXSELF_NARROW},
  {"bvh",         mjFLEXSELF_BVH},
  {"sap",         mjFLEXSELF_SAP},
  {"auto",        mjFLEXSELF_AUTO},
};



//---------------------------------- class mjXReader implementation --------------------------------

// constructor
mjXReader::mjXReader() : schema(MJCF, nMJCF) {
  readingdefaults = false;
}



// print schema
void mjXReader::PrintSchema(std::stringstream& str, bool html, bool pad) {
  if (html) {
    schema.PrintHTML(str, 0, pad);
  } else {
    schema.Print(str, 0);
  }
}



// main entry point for XML parser
//  mjCModel is allocated here; caller is responsible for deallocation
void mjXReader::Parse(XMLElement* root, const mjVFS* vfs) {
  // check schema
  if (!schema.GetError().empty()) {
    throw mjXError(0, "XML Schema Construction Error: %s\n",
                   schema.GetError().c_str());
  }

  // validate
  XMLElement* bad = 0;
  if ((bad = schema.Check(root, 0))) {
    throw mjXError(bad, "Schema violation: %s\n",
                   schema.GetError().c_str());
  }

  // get model name
  string modelname;
  if (ReadAttrTxt(root, "model", modelname)) {
    mjs_setString(spec->modelname, modelname.c_str());
  }

  // get comment
  if (root->FirstChild() && root->FirstChild()->ToComment()) {
    mjs_setString(spec->comment, root->FirstChild()->Value());
  } else {
    mjs_setString(spec->comment, "");
  }

  //------------------- parse MuJoCo sections embedded in all XML formats

  for (XMLElement* section = FirstChildElement(root, "compiler"); section;
       section = NextSiblingElement(section, "compiler")) {
    Compiler(section, spec);
  }

  for (XMLElement* section = FirstChildElement(root, "option"); section;
       section = NextSiblingElement(section, "option")) {
    Option(section, &spec->option);
  }

  for (XMLElement* section = FirstChildElement(root, "size"); section;
       section = NextSiblingElement(section, "size")) {
    Size(section, spec);
  }

  //------------------ parse MJCF-specific sections

  for (XMLElement* section = FirstChildElement(root, "visual"); section;
       section = NextSiblingElement(section, "visual")) {
    Visual(section);
  }

  for (XMLElement* section = FirstChildElement(root, "statistic"); section;
       section = NextSiblingElement(section, "statistic")) {
    Statistic(section);
  }

  readingdefaults = true;
  for (XMLElement* section = FirstChildElement(root, "default"); section;
       section = NextSiblingElement(section, "default")) {
    Default(section, nullptr, vfs);
  }
  readingdefaults = false;

  for (XMLElement* section = FirstChildElement(root, "extension"); section;
       section = NextSiblingElement(section, "extension")) {
    Extension(section);
  }

  for (XMLElement* section = FirstChildElement(root, "custom"); section;
       section = NextSiblingElement(section, "custom")) {
    Custom(section);
  }

  for (XMLElement* section = FirstChildElement(root, "asset"); section;
       section = NextSiblingElement(section, "asset")) {
    Asset(section, vfs);
  }

  for (XMLElement* section = FirstChildElement(root, "contact"); section;
       section = NextSiblingElement(section, "contact")) {
    Contact(section);
  }

  for (XMLElement* section = FirstChildElement(root, "deformable"); section;
       section = NextSiblingElement(section, "deformable")) {
    Deformable(section, vfs);
  }

  for (XMLElement* section = FirstChildElement(root, "equality"); section;
       section = NextSiblingElement(section, "equality")) {
    Equality(section);
  }

  for (XMLElement* section = FirstChildElement(root, "tendon"); section;
       section = NextSiblingElement(section, "tendon")) {
    Tendon(section);
  }

  for (XMLElement* section = FirstChildElement(root, "actuator"); section;
       section = NextSiblingElement(section, "actuator")) {
    Actuator(section);
  }

  for (XMLElement* section = FirstChildElement(root, "sensor"); section;
       section = NextSiblingElement(section, "sensor")) {
    Sensor(section);
  }

  for (XMLElement* section = FirstChildElement(root, "keyframe"); section;
       section = NextSiblingElement(section, "keyframe")) {
    Keyframe(section);
  }

  for (XMLElement* section = FirstChildElement(root, "worldbody"); section;
       section = NextSiblingElement(section, "worldbody")) {
    Body(section, mjs_findBody(spec, "world"), nullptr, vfs);
  }
}



// compiler section parser
void mjXReader::Compiler(XMLElement* section, mjSpec* spec) {
  string text;
  int n;

  // top-level attributes
  if (MapValue(section, "autolimits", &n, bool_map, 2)) {
    spec->autolimits = (n==1);
  }
  ReadAttr(section, "boundmass", 1, &spec->boundmass, text);
  ReadAttr(section, "boundinertia", 1, &spec->boundinertia, text);
  ReadAttr(section, "settotalmass", 1, &spec->settotalmass, text);
  if (MapValue(section, "balanceinertia", &n, bool_map, 2)) {
    spec->balanceinertia = (n==1);
  }
  if (MapValue(section, "strippath", &n, bool_map, 2)) {
    spec->strippath = (n==1);
  }
  if (MapValue(section, "fitaabb", &n, bool_map, 2)) {
    spec->fitaabb = (n==1);
  }
  if (MapValue(section, "coordinate", &n, coordinate_map, 2)) {
    if (n==1) {
      throw mjXError(section, "global coordinates no longer supported. To convert existing models, "
                              "load and save them in MuJoCo 2.3.3 or older");
    }
  }
  if (MapValue(section, "angle", &n, angle_map, 2)) {
    spec->degree = (n==1);
  }
  if (ReadAttrTxt(section, "eulerseq", text)) {
    if (text.size()!=3) {
      throw mjXError(section, "euler format must have length 3");
    }
    memcpy(spec->eulerseq, text.c_str(), 3);
  }
  if (ReadAttrTxt(section, "assetdir", text)) {
    mjs_setString(spec->meshdir, text.c_str());
    mjs_setString(spec->texturedir, text.c_str());
  }
  // meshdir and texturedir take precedence over assetdir
  string meshdir, texturedir;
  if (ReadAttrTxt(section, "meshdir", meshdir)) {
    mjs_setString(spec->meshdir, meshdir.c_str());
  };
  if (ReadAttrTxt(section, "texturedir", texturedir)) {
    mjs_setString(spec->texturedir, texturedir.c_str());
  }
  if (MapValue(section, "discardvisual", &n, bool_map, 2)) {
    spec->discardvisual = (n==1);
  }
  if (MapValue(section, "convexhull", &n, bool_map, 2)) {
    spec->convexhull = (n==1);
  }
  if (MapValue(section, "usethread", &n, bool_map, 2)) {
    spec->usethread = (n==1);
  }
  if (MapValue(section, "fusestatic", &n, bool_map, 2)) {
    spec->fusestatic = (n==1);
  }
  MapValue(section, "inertiafromgeom", &spec->inertiafromgeom, TFAuto_map, 3);
  ReadAttr(section, "inertiagrouprange", 2, spec->inertiagrouprange, text);
  if (MapValue(section, "exactmeshinertia", &n, bool_map, 2)){
    spec->exactmeshinertia = (n==1);
  }

  // lengthrange subelement
  XMLElement* elem = FindSubElem(section, "lengthrange");
  if (elem) {
    mjLROpt* opt = &(spec->LRopt);

    // flags
    MapValue(elem, "mode", &opt->mode, lrmode_map, lrmode_sz);
    if (MapValue(elem, "useexisting", &n, bool_map, 2)) {
      opt->useexisting = (n==1);
    }
    if (MapValue(elem, "uselimit", &n, bool_map, 2)) {
      opt->uselimit = (n==1);
    }

    // algorithm parameters
    ReadAttr(elem, "accel", 1, &opt->accel, text);
    ReadAttr(elem, "maxforce", 1, &opt->maxforce, text);
    ReadAttr(elem, "timeconst", 1, &opt->timeconst, text);
    ReadAttr(elem, "timestep", 1, &opt->timestep, text);
    ReadAttr(elem, "inttotal", 1, &opt->inttotal, text);
    ReadAttr(elem, "interval", 1, &opt->interval, text);
    ReadAttr(elem, "tolrange", 1, &opt->tolrange, text);
  }
}



// option section parser
void mjXReader::Option(XMLElement* section, mjOption* opt) {
  string text;
  int n;

  // read options
  ReadAttr(section, "timestep", 1, &opt->timestep, text);
  ReadAttr(section, "apirate", 1, &opt->apirate, text);
  ReadAttr(section, "impratio", 1, &opt->impratio, text);
  ReadAttr(section, "tolerance", 1, &opt->tolerance, text);
  ReadAttr(section, "ls_tolerance", 1, &opt->ls_tolerance, text);
  ReadAttr(section, "noslip_tolerance", 1, &opt->noslip_tolerance, text);
  ReadAttr(section, "mpr_tolerance", 1, &opt->mpr_tolerance, text);
  ReadAttr(section, "gravity", 3, opt->gravity, text);
  ReadAttr(section, "wind", 3, opt->wind, text);
  ReadAttr(section, "magnetic", 3, opt->magnetic, text);
  ReadAttr(section, "density", 1, &opt->density, text);
  ReadAttr(section, "viscosity", 1, &opt->viscosity, text);

  ReadAttr(section, "o_margin", 1, &opt->o_margin, text);
  ReadAttr(section, "o_solref", mjNREF, opt->o_solref, text, false, false);
  ReadAttr(section, "o_solimp", mjNIMP, opt->o_solimp, text, false, false);
  ReadAttr(section, "o_friction", 5, opt->o_friction, text, false, false);

  MapValue(section, "integrator", &opt->integrator, integrator_map, integrator_sz);
  MapValue(section, "cone", &opt->cone, cone_map, cone_sz);
  MapValue(section, "jacobian", &opt->jacobian, jac_map, jac_sz);
  MapValue(section, "solver", &opt->solver, solver_map, solver_sz);
  ReadAttrInt(section, "iterations", &opt->iterations);
  ReadAttrInt(section, "ls_iterations", &opt->ls_iterations);
  ReadAttrInt(section, "noslip_iterations", &opt->noslip_iterations);
  ReadAttrInt(section, "mpr_iterations", &opt->mpr_iterations);
  ReadAttrInt(section, "sdf_iterations", &opt->sdf_iterations);
  ReadAttrInt(section, "sdf_initpoints", &opt->sdf_initpoints);

  // actuatorgroupdisable
  constexpr int num_bitflags = 31;
  int disabled_act_groups[num_bitflags];
  int num_found = ReadAttr(section, "actuatorgroupdisable", num_bitflags, disabled_act_groups,
                           text, false, false);
  for (int i=0; i < num_found; i++) {
    int group = disabled_act_groups[i];
    if (group < 0) {
      throw mjXError(section, "disabled actuator group value must be non-negative");
    }
    if (group > num_bitflags - 1) {
      throw mjXError(section, "disabled actuator group value cannot exceed 30");
    }
    opt->disableactuator |= (1 << group);
  }

  // read disable sub-element
  XMLElement* elem = FindSubElem(section, "flag");
  if (elem) {
#define READDSBL(NAME, MASK) \
        if (MapValue(elem, NAME, &n, enable_map, 2)) { \
            opt->disableflags ^= (opt->disableflags & MASK); \
            opt->disableflags |= (n ? 0 : MASK); }

    READDSBL("constraint",   mjDSBL_CONSTRAINT)
    READDSBL("equality",     mjDSBL_EQUALITY)
    READDSBL("frictionloss", mjDSBL_FRICTIONLOSS)
    READDSBL("limit",        mjDSBL_LIMIT)
    READDSBL("contact",      mjDSBL_CONTACT)
    READDSBL("passive",      mjDSBL_PASSIVE)
    READDSBL("gravity",      mjDSBL_GRAVITY)
    READDSBL("clampctrl",    mjDSBL_CLAMPCTRL)
    READDSBL("warmstart",    mjDSBL_WARMSTART)
    READDSBL("filterparent", mjDSBL_FILTERPARENT)
    READDSBL("actuation",    mjDSBL_ACTUATION)
    READDSBL("refsafe",      mjDSBL_REFSAFE)
    READDSBL("sensor",       mjDSBL_SENSOR)
    READDSBL("midphase",     mjDSBL_MIDPHASE)
    READDSBL("eulerdamp",    mjDSBL_EULERDAMP)
    READDSBL("autoreset",    mjDSBL_AUTORESET)
#undef READDSBL

#define READENBL(NAME, MASK) \
        if (MapValue(elem, NAME, &n, enable_map, 2)) { \
            opt->enableflags ^= (opt->enableflags & MASK); \
            opt->enableflags |= (n ? MASK : 0); }

    READENBL("override",    mjENBL_OVERRIDE)
    READENBL("energy",      mjENBL_ENERGY)
    READENBL("fwdinv",      mjENBL_FWDINV)
    READENBL("invdiscrete", mjENBL_INVDISCRETE)
    READENBL("multiccd",    mjENBL_MULTICCD)
    READENBL("island",      mjENBL_ISLAND)
#undef READENBL
  }
}



// size section parser
void mjXReader::Size(XMLElement* section, mjSpec* spec) {
  // read memory bytes
  {
    constexpr char err_msg[] =
        "unsigned integer with an optional suffix {K,M,G,T,P,E} is expected in "
        "attribute 'memory' (or the size specified is too big)";

    auto memory = [&]() -> std::optional<std::size_t> {
      const char* pstr = section->Attribute("memory");
      if (!pstr) {
        return std::nullopt;
      }

      // trim entire string
      string trimmed;
      {
        std::istringstream strm((string(pstr)));
        strm >> trimmed;
        string trailing;
        strm >> trailing;
        if (!trailing.empty() || !strm.eof()) {
          throw mjXError(section, "%s", err_msg);
        }

        // allow explicit specification of the default "-1" value
        if (trimmed == "-1") {
          return std::nullopt;
        }
      }

      std::istringstream strm(trimmed);

      // check that the number is not negative
      if (strm.peek() == '-') {
        throw mjXError(section, "%s", err_msg);
      }

      std::size_t base_size;
      strm >> base_size;
      if (strm.fail()) {
        // either not an integer or the number without the suffix is already bigger than size_t
        throw mjXError(section, "%s", err_msg);
      }

      // parse the multiplier suffix
      int multiplier_bit = 0;
      if (!strm.eof()) {
        char suffix = strm.get();
        if (suffix == 'K' || suffix == 'k') {
          multiplier_bit = 10;
        } else if (suffix == 'M' || suffix == 'm') {
          multiplier_bit = 20;
        } else if (suffix == 'G' || suffix == 'g') {
          multiplier_bit = 30;
        } else if (suffix == 'T' || suffix == 't') {
          multiplier_bit = 40;
        } else if (suffix == 'P' || suffix == 'p') {
          multiplier_bit = 50;
        } else if (suffix == 'E' || suffix == 'e') {
          multiplier_bit = 60;
        }

        // check for invalid suffix, or suffix longer than one character
        strm.get();
        if (!multiplier_bit || !strm.eof()) {
          throw mjXError(section, "%s", err_msg);
        }
      }

      // check that the specified suffix isn't bigger than size_t
      if (multiplier_bit + 1 > std::numeric_limits<std::size_t>::digits) {
        throw mjXError(section, "%s", err_msg);
      }

      // check that the suffix won't take the total size beyond size_t
      const std::size_t max_base_size =
          (std::numeric_limits<std::size_t>::max() << multiplier_bit) >> multiplier_bit;
      if (base_size > max_base_size) {
        throw mjXError(section, "%s", err_msg);
      }

      const std::size_t total_size = base_size << multiplier_bit;
      return total_size;
    }();

    if (memory.has_value()) {
      if (*memory / sizeof(mjtNum) > std::numeric_limits<std::size_t>::max()) {
        throw mjXError(section, "%s", err_msg);
      }
      spec->memory = *memory;
    }
  }

  // read sizes
  ReadAttrInt(section, "nuserdata", &spec->nuserdata);
  ReadAttrInt(section, "nkey", &spec->nkey);

  ReadAttrInt(section, "nconmax", &spec->nconmax);
  if (spec->nconmax < -1) throw mjXError(section, "nconmax must be >= -1");

  {
    int nstack = -1;
    const bool has_nstack = ReadAttrInt(section, "nstack", &nstack);
    if (has_nstack) {
      if (spec->nstack < -1) {
        throw mjXError(section, "nstack must be >= -1");
      }
      if (spec->memory != -1 && nstack != -1) {
        throw mjXError(section,
                       "either 'memory' and 'nstack' attribute can be specified, not both");
      }
      spec->nstack = nstack;
    }
  }
  {
    int njmax = -1;
    const bool has_njmax = ReadAttrInt(section, "njmax", &njmax);
    if (has_njmax) {
      if (spec->njmax < -1) {
        throw mjXError(section, "njmax must be >= -1");
      }
      if (spec->memory != -1 && njmax != -1) {
        throw mjXError(section,
                       "either 'memory' and 'njmax' attribute can be specified, not both");
      }
      spec->njmax = njmax;
    }
  }

  ReadAttrInt(section, "nuser_body", &spec->nuser_body);
  if (spec->nuser_body < -1) throw mjXError(section, "nuser_body must be >= -1");

  ReadAttrInt(section, "nuser_jnt", &spec->nuser_jnt);
  if (spec->nuser_jnt < -1) throw mjXError(section, "nuser_jnt must be >= -1");

  ReadAttrInt(section, "nuser_geom", &spec->nuser_geom);
  if (spec->nuser_geom < -1) throw mjXError(section, "nuser_geom must be >= -1");

  ReadAttrInt(section, "nuser_site", &spec->nuser_site);
  if (spec->nuser_site < -1) throw mjXError(section, "nuser_site must be >= -1");

  ReadAttrInt(section, "nuser_cam", &spec->nuser_cam);
  if (spec->nuser_cam < -1) throw mjXError(section, "nuser_cam must be >= -1");

  ReadAttrInt(section, "nuser_tendon", &spec->nuser_tendon);
  if (spec->nuser_tendon < -1) throw mjXError(section, "nuser_tendon must be >= -1");

  ReadAttrInt(section, "nuser_actuator", &spec->nuser_actuator);
  if (spec->nuser_actuator < -1) throw mjXError(section, "nuser_actuator must be >= -1");

  ReadAttrInt(section, "nuser_sensor", &spec->nuser_sensor);
  if (spec->nuser_sensor < -1) throw mjXError(section, "nuser_sensor must be >= -1");
}



// statistic section parser
void mjXReader::Statistic(XMLElement* section) {
  string text;

  // read statistics
  ReadAttr(section, "meaninertia", 1, &spec->stat.meaninertia, text);
  ReadAttr(section, "meanmass", 1, &spec->stat.meanmass, text);
  ReadAttr(section, "meansize", 1, &spec->stat.meansize, text);
  ReadAttr(section, "extent", 1, &spec->stat.extent, text);
  if (mjuu_defined(spec->stat.extent) && spec->stat.extent<=0) {
    throw mjXError(section, "extent must be strictly positive");
  }
  ReadAttr(section, "center", 3, spec->stat.center, text);
}



//---------------------------------- one-element parsers -------------------------------------------

// flex element parser
void mjXReader::OneFlex(XMLElement* elem, mjsFlex* flex) {
  string text, name, material;
  int n;

  // read attributes
  if (ReadAttrTxt(elem, "name", name)) {
    mjs_setString(flex->name, name.c_str());
  }
  if (ReadAttrTxt(elem, "material", material)) {
    mjs_setString(flex->material, material.c_str());
  }

  ReadAttr(elem, "radius", 1, &flex->radius, text);
  ReadAttr(elem, "rgba", 4, flex->rgba, text);
  if (MapValue(elem, "flatskin", &n, bool_map, 2)) {
    flex->flatskin = (n==1);
  }
  ReadAttrInt(elem, "dim", &flex->dim);
  ReadAttrInt(elem, "group", &flex->group);

  // read data vectors
  if (ReadAttrTxt(elem, "body", text, true)) {
    mjs_setStringVec(flex->vertbody, text.c_str());
  }
  auto vert = ReadAttrVec<double>(elem, "vertex");
  if (vert.has_value()) {
    mjs_setDouble(flex->vert, vert->data(), vert->size());
  }
  auto element = ReadAttrVec<int>(elem, "element", true);
  if (element.has_value()) {
    mjs_setInt(flex->elem, element->data(), element->size());
  }
  auto texcoord = ReadAttrVec<float>(elem, "texcoord");
  if (texcoord.has_value()) {
    mjs_setFloat(flex->texcoord, texcoord->data(), texcoord->size());
  }

  // contact subelement
  XMLElement* cont = FirstChildElement(elem, "contact");
  if (cont) {
    ReadAttrInt(cont, "contype", &flex->contype);
    ReadAttrInt(cont, "conaffinity", &flex->conaffinity);
    ReadAttrInt(cont, "condim", &flex->condim);
    ReadAttrInt(cont, "priority", &flex->priority);
    ReadAttr(cont, "friction", 3, flex->friction, text, false, false);
    ReadAttr(cont, "solmix", 1, &flex->solmix, text);
    ReadAttr(cont, "solref", mjNREF, flex->solref, text, false, false);
    ReadAttr(cont, "solimp", mjNIMP, flex->solimp, text, false, false);
    ReadAttr(cont, "margin", 1, &flex->margin, text);
    ReadAttr(cont, "gap", 1, &flex->gap, text);
    if (MapValue(cont, "internal", &n, bool_map, 2)) {
      flex->internal = (n==1);
    }
    MapValue(cont, "selfcollide", &flex->selfcollide, flexself_map, 5);
    ReadAttrInt(cont, "activelayers", &flex->activelayers);
  }

  // edge subelement
  XMLElement* edge = FirstChildElement(elem, "edge");
  if (edge) {
    ReadAttr(edge, "stiffness", 1, &flex->edgestiffness, text);
    ReadAttr(edge, "damping", 1, &flex->edgedamping, text);
  }

  // write error info
  mjs_setString(flex->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// mesh element parser
void mjXReader::OneMesh(XMLElement* elem, mjsMesh* mesh, const mjVFS* vfs) {
  int n;
  string text, name, content_type;

  // read attributes
  if (ReadAttrTxt(elem, "name", name)) {
    *mesh->name = name;
  }
  if (ReadAttrTxt(elem, "content_type", content_type)) {
    *mesh->content_type = content_type;
  }
  auto file = ReadAttrFile(elem, "file", vfs, MeshDir());
  if (file) {
    mjs_setString(mesh->file, file->c_str());
  }
  ReadAttr(elem, "refpos", 3, mesh->refpos, text);
  ReadAttr(elem, "refquat", 4, mesh->refquat, text);
  ReadAttr(elem, "scale", 3, mesh->scale, text);

  XMLElement* eplugin = FirstChildElement(elem, "plugin");
  if (eplugin) {
    OnePlugin(eplugin, &mesh->plugin);
  }

  if (MapValue(elem, "smoothnormal", &n, bool_map, 2)) {
    mesh->smoothnormal = (n==1);
  }

  if (ReadAttrInt(elem, "maxhullvert", &n)) {
    if (n != 0 && n < 4) throw mjXError(elem, "maxhullvert must be larger than 3");
    mesh->maxhullvert = n;
  }

  // read user vertex data
  if (ReadAttrTxt(elem, "vertex", text)) {
    auto uservert = ReadAttrVec<float>(elem, "vertex");
    if (uservert.has_value()) {
      mjs_setFloat(mesh->uservert, uservert->data(), uservert->size());
    }
  }

  // read user normal data
  if (ReadAttrTxt(elem, "normal", text)) {
    auto usernormal = ReadAttrVec<float>(elem, "normal");
    if (usernormal.has_value()) {
      mjs_setFloat(mesh->usernormal, usernormal->data(), usernormal->size());
    }
  }

  // read user texcoord data
  if (ReadAttrTxt(elem, "texcoord", text)) {
    auto usertexcoord = ReadAttrVec<float>(elem, "texcoord");
    if (usertexcoord.has_value()) {
      mjs_setFloat(mesh->usertexcoord, usertexcoord->data(), usertexcoord->size());
    }
  }

  // read user face data
  if (ReadAttrTxt(elem, "face", text)) {
    auto userface = ReadAttrVec<int>(elem, "face");
    if (userface.has_value()) {
      mjs_setInt(mesh->userface, userface->data(), userface->size());
    }
  }

  // write error info
  mjs_setString(mesh->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// skin element parser
void mjXReader::OneSkin(XMLElement* elem, mjsSkin* skin, const mjVFS* vfs) {
  string text, name, material;
  float data[4];

  // read attributes
  if (ReadAttrTxt(elem, "name", name)) {
    mjs_setString(skin->name, name.c_str());
  }
  auto file = ReadAttrFile(elem, "file", vfs, AssetDir());
  if (file.has_value()) {
    mjs_setString(skin->file, file->c_str());
  }
  if (ReadAttrTxt(elem, "material", material)) {
    mjs_setString(skin->material, material.c_str());
}
  ReadAttrInt(elem, "group", &skin->group);
  if (skin->group<0 || skin->group>=mjNGROUP) {
    throw mjXError(elem, "skin group must be between 0 and 5");
  }
  ReadAttr(elem, "rgba", 4, skin->rgba, text);
  ReadAttr(elem, "inflate", 1, &skin->inflate, text);

  // read vertex data
  auto vertex = ReadAttrVec<float>(elem, "vertex");
  if (vertex.has_value()) {
    mjs_setFloat(skin->vert, vertex->data(), vertex->size());
  }

  // read texcoord data
  auto texcoord = ReadAttrVec<float>(elem, "texcoord");
  if (texcoord.has_value()) {
    mjs_setFloat(skin->texcoord, texcoord->data(), texcoord->size());
  }

  // read user face data
  auto face = ReadAttrVec<int>(elem, "face");
  if (face.has_value()) {
    mjs_setInt(skin->face, face->data(), face->size());
  }

  // read bones
  XMLElement* bone = FirstChildElement(elem, "bone");
  std::vector<float> bindpos;
  std::vector<float> bindquat;

  while (bone) {
    // read body
    ReadAttrTxt(bone, "body", text, true);
    mjs_appendString(skin->bodyname, text.c_str());

    // read bindpos
    ReadAttr(bone, "bindpos", 3, data, text, true);
    bindpos.push_back(data[0]);
    bindpos.push_back(data[1]);
    bindpos.push_back(data[2]);

    // read bindquat
    ReadAttr(bone, "bindquat", 4, data, text, true);
    bindquat.push_back(data[0]);
    bindquat.push_back(data[1]);
    bindquat.push_back(data[2]);
    bindquat.push_back(data[3]);

    // read vertid
    auto tempid = ReadAttrVec<int>(bone, "vertid", true);
    if (tempid.has_value()) {
      mjs_appendIntVec(skin->vertid, tempid->data(), tempid->size());
    }

    // read vertweight
    auto tempweight = ReadAttrVec<float>(bone, "vertweight", true);
    if (tempweight.has_value()) {
      mjs_appendFloatVec(skin->vertweight, tempweight->data(), tempweight->size());
    }

    // advance to next bone
    bone = NextSiblingElement(bone, "bone");
  }

  // set bind vectors
  mjs_setFloat(skin->bindpos, bindpos.data(), bindpos.size());
  mjs_setFloat(skin->bindquat, bindquat.data(), bindquat.size());

  // write error info
  mjs_setString(skin->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// material element parser
void mjXReader::OneMaterial(XMLElement* elem, mjsMaterial* material) {
  string text, name, texture;
  int n;

  // read attributes
  if (ReadAttrTxt(elem, "name", name)) {
    mjs_setString(material->name, name.c_str());
  }

  bool tex_attributes_found = false;
  if (ReadAttrTxt(elem, "texture", texture)) {
    mjs_setInStringVec(material->textures, mjTEXROLE_RGB, texture.c_str());
    tex_attributes_found = true;
  }

  XMLElement* tex_elem = FirstChildElement(elem);
  while (tex_elem) {
    if (tex_attributes_found) {
      throw mjXError(tex_elem, "A material with a texture attribute cannot have texture sub-elements");
    }
    // texture sub-element
    int role = FindKey(texrole_map, texrole_sz, tex_elem->Name());
    string texmat;
    ReadAttrTxt(tex_elem, "texture", texmat, true);
    mjs_setInStringVec(material->textures, role, texmat.c_str());
    tex_elem = NextSiblingElement(tex_elem);
  }

  if (MapValue(elem, "texuniform", &n, bool_map, 2)) {
    material->texuniform = (n==1);
  }
  ReadAttr(elem, "texrepeat", 2, material->texrepeat, text);
  ReadAttr(elem, "emission", 1, &material->emission, text);
  ReadAttr(elem, "specular", 1, &material->specular, text);
  ReadAttr(elem, "shininess", 1, &material->shininess, text);
  ReadAttr(elem, "reflectance", 1, &material->reflectance, text);
  ReadAttr(elem, "metallic", 1, &material->metallic, text);
  ReadAttr(elem, "roughness", 1, &material->roughness, text);
  ReadAttr(elem, "rgba", 4, material->rgba, text);

  // write error info
  mjs_setString(material->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// joint element parser
void mjXReader::OneJoint(XMLElement* elem, mjsJoint* joint) {
  string text, name;
  std::vector<double> userdata;
  int n;

  // read attributes
  if (ReadAttrTxt(elem, "name", name)) {
    mjs_setString(joint->name, name.c_str());
  }
  if (MapValue(elem, "type", &n, joint_map, joint_sz)) {
    joint->type = (mjtJoint)n;
  }
  MapValue(elem, "limited", &joint->limited, TFAuto_map, 3);
  MapValue(elem, "actuatorfrclimited", &joint->actfrclimited, TFAuto_map, 3);
  ReadAttrInt(elem, "group", &joint->group);
  ReadAttr(elem, "solreflimit", mjNREF, joint->solref_limit, text, false, false);
  ReadAttr(elem, "solimplimit", mjNIMP, joint->solimp_limit, text, false, false);
  ReadAttr(elem, "solreffriction", mjNREF, joint->solref_friction, text, false, false);
  ReadAttr(elem, "solimpfriction", mjNIMP, joint->solimp_friction, text, false, false);
  ReadAttr(elem, "pos", 3, joint->pos, text);
  ReadAttr(elem, "axis", 3, joint->axis, text);
  ReadAttr(elem, "springdamper", 2, joint->springdamper, text);
  ReadAttr(elem, "stiffness", 1, &joint->stiffness, text);
  ReadAttr(elem, "range", 2, joint->range, text);
  ReadAttr(elem, "actuatorfrcrange", 2, joint->actfrcrange, text);
  ReadAttr(elem, "margin", 1, &joint->margin, text);
  ReadAttr(elem, "ref", 1, &joint->ref, text);
  ReadAttr(elem, "springref", 1, &joint->springref, text);
  ReadAttr(elem, "armature", 1, &joint->armature, text);
  ReadAttr(elem, "damping", 1, &joint->damping, text);
  ReadAttr(elem, "frictionloss", 1, &joint->frictionloss, text);
  if (MapValue(elem, "actuatorgravcomp", &n, bool_map, 2)) {
    joint->actgravcomp = (n==1);
  }

  // read userdata
  if (ReadVector(elem, "user", userdata, text)) {
    mjs_setDouble(joint->userdata, userdata.data(), userdata.size());
  }

  // write error info
  mjs_setString(joint->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// geom element parser
void mjXReader::OneGeom(XMLElement* elem, mjsGeom* geom) {
  string text, name;
  std::vector<double> userdata;
  string hfieldname, meshname, material;
  int n;

  // read attributes
  if (ReadAttrTxt(elem, "name", name)) {
    mjs_setString(geom->name, name.c_str());
  }
  if (MapValue(elem, "type", &n, geom_map, mjNGEOMTYPES)) {
    geom->type = (mjtGeom)n;
  }
  ReadAttr(elem, "size", 3, geom->size, text, false, false);
  ReadAttrInt(elem, "contype", &geom->contype);
  ReadAttrInt(elem, "conaffinity", &geom->conaffinity);
  ReadAttrInt(elem, "condim", &geom->condim);
  ReadAttrInt(elem, "group", &geom->group);
  ReadAttrInt(elem, "priority", &geom->priority);
  ReadAttr(elem, "friction", 3, geom->friction, text, false, false);
  ReadAttr(elem, "solmix", 1, &geom->solmix, text);
  ReadAttr(elem, "solref", mjNREF, geom->solref, text, false, false);
  ReadAttr(elem, "solimp", mjNIMP, geom->solimp, text, false, false);
  ReadAttr(elem, "margin", 1, &geom->margin, text);
  ReadAttr(elem, "gap", 1, &geom->gap, text);
  if (ReadAttrTxt(elem, "hfield", hfieldname)) {
    mjs_setString(geom->hfieldname, hfieldname.c_str());
  }
  if (ReadAttrTxt(elem, "mesh", meshname)) {
    mjs_setString(geom->meshname, meshname.c_str());
  }
  ReadAttr(elem, "fitscale", 1, &geom->fitscale, text);
  if (ReadAttrTxt(elem, "material", material)) {
    mjs_setString(geom->material, material.c_str());
  }
  ReadAttr(elem, "rgba", 4, geom->rgba, text);
  if (MapValue(elem, "fluidshape", &n, fluid_map, 2)) {
    geom->fluid_ellipsoid = (n == 1);
  }
  ReadAttr(elem, "fluidcoef", 5, geom->fluid_coefs, text, false, false);

  // read userdata
  if (ReadVector(elem, "user", userdata, text)) {
    mjs_setDouble(geom->userdata, userdata.data(), userdata.size());
  }

  // plugin sub-element
  XMLElement* eplugin = FirstChildElement(elem, "plugin");
  if (eplugin) {
    OnePlugin(eplugin, &geom->plugin);
  }

  // remaining attributes
  ReadAttr(elem, "mass", 1, &geom->mass, text);
  ReadAttr(elem, "density", 1, &geom->density, text);
  ReadAttr(elem, "fromto", 6, geom->fromto, text);
  ReadAttr(elem, "pos", 3, geom->pos, text);
  ReadQuat(elem, "quat", geom->quat, text);
  ReadAlternative(elem, geom->alt);

  // compute inertia using either solid or shell geometry
  if (MapValue(elem, "shellinertia", &n, meshtype_map, 2)) {
    geom->typeinertia = (mjtGeomInertia)n;
  }

  // write error info
  mjs_setString(geom->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// site element parser
void mjXReader::OneSite(XMLElement* elem, mjsSite* site) {
  int n;
  string text, name;
  std::vector<double> userdata;
  string material;

  // read attributes
  if (ReadAttrTxt(elem, "name", name)) {
    mjs_setString(site->name, name.c_str());
  }
  if (MapValue(elem, "type", &n, geom_map, mjNGEOMTYPES)) {
    site->type = (mjtGeom)n;
  }
  ReadAttr(elem, "size", 3, site->size, text, false, false);
  ReadAttrInt(elem, "group", &site->group);
  ReadAttr(elem, "pos", 3, site->pos, text);
  ReadQuat(elem, "quat", site->quat, text);
  if (ReadAttrTxt(elem, "material", material)) {
    mjs_setString(site->material, material.c_str());
  }
  ReadAttr(elem, "rgba", 4, site->rgba, text);
  ReadAttr(elem, "fromto", 6, site->fromto, text);
  ReadAlternative(elem, site->alt);
  if (ReadVector(elem, "user", userdata, text)) {
    mjs_setDouble(site->userdata, userdata.data(), userdata.size());
  }

  // write error info
  mjs_setString(site->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// camera element parser
void mjXReader::OneCamera(XMLElement* elem, mjsCamera* camera) {
  int n;
  string text, name, targetbody;
  std::vector<double> userdata;

  // read attributes
  if (ReadAttrTxt(elem, "name", name)) {
    mjs_setString(camera->name, name.c_str());
  }
  if (ReadAttrTxt(elem, "target", targetbody)) {
    mjs_setString(camera->targetbody, targetbody.c_str());
  }
  if (MapValue(elem, "mode", &n, camlight_map, camlight_sz)) {
    camera->mode = (mjtCamLight)n;
  }
  ReadAttr(elem, "pos", 3, camera->pos, text);
  ReadQuat(elem, "quat", camera->quat, text);
  ReadAlternative(elem, camera->alt);
  ReadAttr(elem, "ipd", 1, &camera->ipd, text);

  if (MapValue(elem, "orthographic", &n, bool_map, 2)) {
    camera->orthographic = (n==1);
  }

  bool has_principal = ReadAttr(elem, "principalpixel", 2, camera->principal_pixel, text) ||
                       ReadAttr(elem, "principal", 2, camera->principal_length, text);
  bool has_focal = ReadAttr(elem, "focalpixel", 2, camera->focal_pixel, text) ||
                   ReadAttr(elem, "focal", 2, camera->focal_length, text);
  bool needs_sensorsize = has_principal || has_focal;
  bool has_sensorsize = ReadAttr(elem, "sensorsize", 2, camera->sensor_size, text, needs_sensorsize);
  bool has_fovy = ReadAttr(elem, "fovy", 1, &camera->fovy, text);
  bool needs_resolution = has_focal || has_sensorsize;
  ReadAttr(elem, "resolution", 2, camera->resolution, text, needs_resolution);

  if (camera->resolution[0] < 0 || camera->resolution[1] < 0) {
    throw mjXError(elem, "camera resolution cannot be negative");
  }

  if (has_fovy && has_sensorsize) {
    throw mjXError(
        elem,
        "either 'fovy' or 'sensorsize' attribute can be specified, not both");
  }

  // read userdata
  ReadVector(elem, "user", userdata, text);
  mjs_setDouble(camera->userdata, userdata.data(), userdata.size());

  // write error info
  mjs_setString(camera->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// light element parser
void mjXReader::OneLight(XMLElement* elem, mjsLight* light) {
  int n;
  string text, name, targetbody;

  // read attributes
  if (ReadAttrTxt(elem, "name", name)) {
    mjs_setString(light->name, name.c_str());
  }
  if (ReadAttrTxt(elem, "target", targetbody)) {
    mjs_setString(light->targetbody, targetbody.c_str());
  }
  if (MapValue(elem, "mode", &n, camlight_map, camlight_sz)) {
    light->mode = (mjtCamLight)n;
  }
  if (MapValue(elem, "directional", &n, bool_map, 2)) {
    light->directional = (n==1);
  }
  if (MapValue(elem, "castshadow", &n, bool_map, 2)) {
    light->castshadow = (n==1);
  }
  if (MapValue(elem, "active", &n, bool_map, 2)) {
    light->active = (n==1);
  }
  ReadAttr(elem, "pos", 3, light->pos, text);
  ReadAttr(elem, "dir", 3, light->dir, text);
  ReadAttr(elem, "bulbradius", 1, &light->bulbradius, text);
  ReadAttr(elem, "attenuation", 3, light->attenuation, text);
  ReadAttr(elem, "cutoff", 1, &light->cutoff, text);
  ReadAttr(elem, "exponent", 1, &light->exponent, text);
  ReadAttr(elem, "ambient", 3, light->ambient, text);
  ReadAttr(elem, "diffuse", 3, light->diffuse, text);
  ReadAttr(elem, "specular", 3, light->specular, text);

  // write error info
  mjs_setString(light->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// pair element parser
void mjXReader::OnePair(XMLElement* elem, mjsPair* pair) {
  string text, name, geomname1, geomname2;

  // regular only
  if (!readingdefaults) {
    if (ReadAttrTxt(elem, "geom1", geomname1)) {
      mjs_setString(pair->geomname1, geomname1.c_str());
    }
    if (ReadAttrTxt(elem, "geom2", geomname2)) {
      mjs_setString(pair->geomname2, geomname2.c_str());
    }
  }

  // read other parameters
  if (ReadAttrTxt(elem, "name", name)) {
    mjs_setString(pair->name, name.c_str());
  }
  ReadAttrInt(elem, "condim", &pair->condim);
  ReadAttr(elem, "solref", mjNREF, pair->solref, text, false, false);
  ReadAttr(elem, "solreffriction", mjNREF, pair->solreffriction, text, false, false);
  ReadAttr(elem, "solimp", mjNIMP, pair->solimp, text, false, false);
  ReadAttr(elem, "margin", 1, &pair->margin, text);
  ReadAttr(elem, "gap", 1, &pair->gap, text);
  ReadAttr(elem, "friction", 5, pair->friction, text, false, false);

  // write error info
  mjs_setString(pair->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// equality element parser
void mjXReader::OneEquality(XMLElement* elem, mjsEquality* equality) {
  int n;
  string text, name1, name2, name;

  // read type (bad keywords already detected by schema)
  text = elem->Value();
  equality->type = (mjtEq)FindKey(equality_map, equality_sz, text);

  // regular only
  if (!readingdefaults) {
    if (ReadAttrTxt(elem, "name", name)) {
      mjs_setString(equality->name, name.c_str());
    }

    switch (equality->type) {
    case mjEQ_CONNECT:
      ReadAttrTxt(elem, "body1", name1, true);
      ReadAttrTxt(elem, "body2", name2);
      ReadAttr(elem, "anchor", 3, equality->data, text, true);
      break;

    case mjEQ_WELD:
      ReadAttrTxt(elem, "body1", name1, true);
      ReadAttrTxt(elem, "body2", name2);
      ReadAttr(elem, "relpose", 7, equality->data+3, text);
      ReadAttr(elem, "torquescale", 1, equality->data+10, text);
      if (!ReadAttr(elem, "anchor", 3, equality->data, text)) {
        mjuu_zerovec(equality->data, 3);
      }
      break;

    case mjEQ_JOINT:
      ReadAttrTxt(elem, "joint1", name1, true);
      ReadAttrTxt(elem, "joint2", name2);
      ReadAttr(elem, "polycoef", 5, equality->data, text, false, false);
      break;

    case mjEQ_TENDON:
      ReadAttrTxt(elem, "tendon1", name1, true);
      ReadAttrTxt(elem, "tendon2", name2);
      ReadAttr(elem, "polycoef", 5, equality->data, text, false, false);
      break;

    case mjEQ_FLEX:
      ReadAttrTxt(elem, "flex", name1, true);
      break;

    case mjEQ_DISTANCE:
      throw mjXError(elem, "support for distance equality constraints was removed in MuJoCo 2.2.2");
      break;

    default:                    // SHOULD NOT OCCUR
      throw mjXError(elem, "unrecognized equality constraint type");
    }

    mjs_setString(equality->name1, name1.c_str());
    if (!name2.empty()) {
      mjs_setString(equality->name2, name2.c_str());
    }
  }

  // read attributes
  if (MapValue(elem, "active", &n, bool_map, 2)) {
    equality->active = (n==1);
  }
  ReadAttr(elem, "solref", mjNREF, equality->solref, text, false, false);
  ReadAttr(elem, "solimp", mjNIMP, equality->solimp, text, false, false);

  // write error info
  mjs_setString(equality->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// tendon element parser
void mjXReader::OneTendon(XMLElement* elem, mjsTendon* tendon) {
  string text, name, material;
  std::vector<double> userdata;

  // read attributes
  if (ReadAttrTxt(elem, "name", name)) {
    mjs_setString(tendon->name, name.c_str());
  }
  ReadAttrInt(elem, "group", &tendon->group);
  if (ReadAttrTxt(elem, "material", material)) {
    mjs_setString(tendon->material, material.c_str());
  }
  MapValue(elem, "limited", &tendon->limited, TFAuto_map, 3);
  ReadAttr(elem, "width", 1, &tendon->width, text);
  ReadAttr(elem, "solreflimit", mjNREF, tendon->solref_limit, text, false, false);
  ReadAttr(elem, "solimplimit", mjNIMP, tendon->solimp_limit, text, false, false);
  ReadAttr(elem, "solreffriction", mjNREF, tendon->solref_friction, text, false, false);
  ReadAttr(elem, "solimpfriction", mjNIMP, tendon->solimp_friction, text, false, false);
  ReadAttr(elem, "range", 2, tendon->range, text);
  ReadAttr(elem, "margin", 1, &tendon->margin, text);
  ReadAttr(elem, "stiffness", 1, &tendon->stiffness, text);
  ReadAttr(elem, "damping", 1, &tendon->damping, text);
  ReadAttr(elem, "frictionloss", 1, &tendon->frictionloss, text);
  // read springlength, either one or two values; if one, copy to second value
  if (ReadAttr(elem, "springlength", 2, tendon->springlength, text, false, false) == 1) {
    tendon->springlength[1] = tendon->springlength[0];
  }
  ReadAttr(elem, "rgba", 4, tendon->rgba, text);

  // read userdata
  if (ReadVector(elem, "user", userdata, text)) {
    mjs_setDouble(tendon->userdata, userdata.data(), userdata.size());
  }

  // write error info
  mjs_setString(tendon->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// actuator element parser
void mjXReader::OneActuator(XMLElement* elem, mjsActuator* actuator) {
  string text, type, name, target, slidersite, refsite;

  // common attributes
  if (ReadAttrTxt(elem, "name", name)) {
    mjs_setString(actuator->name, name.c_str());
  }
  ReadAttrInt(elem, "group", &actuator->group);
  MapValue(elem, "ctrllimited", &actuator->ctrllimited, TFAuto_map, 3);
  MapValue(elem, "forcelimited", &actuator->forcelimited, TFAuto_map, 3);
  MapValue(elem, "actlimited", &actuator->actlimited, TFAuto_map, 3);
  ReadAttr(elem, "ctrlrange", 2, actuator->ctrlrange, text);
  ReadAttr(elem, "forcerange", 2, actuator->forcerange, text);
  ReadAttr(elem, "actrange", 2, actuator->actrange, text);
  ReadAttr(elem, "lengthrange", 2, actuator->lengthrange, text);
  ReadAttr(elem, "gear", 6, actuator->gear, text, false, false);

  // transmission target and type
  int cnt = 0;
  if (ReadAttrTxt(elem, "joint", target)) {
    mjs_setString(actuator->target, target.c_str());
    actuator->trntype = mjTRN_JOINT;
    cnt++;
  }
  if (ReadAttrTxt(elem, "jointinparent", target)) {
    mjs_setString(actuator->target, target.c_str());
    actuator->trntype = mjTRN_JOINTINPARENT;
    cnt++;
  }
  if (ReadAttrTxt(elem, "tendon", target)) {
    mjs_setString(actuator->target, target.c_str());
    actuator->trntype = mjTRN_TENDON;
    cnt++;
  }
  if (ReadAttrTxt(elem, "cranksite", target)) {
    mjs_setString(actuator->target, target.c_str());
    actuator->trntype = mjTRN_SLIDERCRANK;
    cnt++;
  }
  if (ReadAttrTxt(elem, "site", target)) {
    mjs_setString(actuator->target, target.c_str());
    actuator->trntype = mjTRN_SITE;
    cnt++;
  }
  if (ReadAttrTxt(elem, "body", target)) {
    mjs_setString(actuator->target, target.c_str());
    actuator->trntype = mjTRN_BODY;
    cnt++;
  }
  // check for repeated transmission
  if (cnt>1) {
    throw mjXError(elem, "actuator can have at most one of transmission target");
  }

  // slidercrank-specific parameters
  int r1 = ReadAttr(elem, "cranklength", 1, &actuator->cranklength, text);
  int r2 = ReadAttrTxt(elem, "slidersite", slidersite);
  if (r2) {
    mjs_setString(actuator->slidersite, slidersite.c_str());
  }
  if ((r1 || r2) && actuator->trntype!=mjTRN_SLIDERCRANK && actuator->trntype!=mjTRN_UNDEFINED) {
    throw mjXError(elem, "cranklength and slidersite can only be used in slidercrank transmission");
  }

  // site-specific parameters (refsite)
  int r3 = ReadAttrTxt(elem, "refsite", refsite);
  if (r3) {
    mjs_setString(actuator->refsite, refsite.c_str());
  }
  if (r3 && actuator->trntype!=mjTRN_SITE && actuator->trntype!=mjTRN_UNDEFINED) {
    throw mjXError(elem, "refsite can only be used with site transmission");
  }

  // get predefined type
  type = elem->Value();

  // explicit attributes
  if (type=="general") {
    // explicit attributes
    int n;
    if (MapValue(elem, "dyntype", &n, dyn_map, dyn_sz)) {
      actuator->dyntype = (mjtDyn)n;
    }
    if (MapValue(elem, "gaintype", &n, gain_map, gain_sz)) {
      actuator->gaintype = (mjtGain)n;
    }
    if (MapValue(elem, "biastype", &n, bias_map, bias_sz)) {
      actuator->biastype = (mjtBias)n;
    }
    if (MapValue(elem, "actearly", &n, bool_map, 2)) {
      actuator->actearly = (n==1);
    }
    ReadAttr(elem, "dynprm", mjNDYN, actuator->dynprm, text, false, false);
    ReadAttr(elem, "gainprm", mjNGAIN, actuator->gainprm, text, false, false);
    ReadAttr(elem, "biasprm", mjNBIAS, actuator->biasprm, text, false, false);
    ReadAttrInt(elem, "actdim", &actuator->actdim);
  }

  // direct drive motor
  else if (type=="motor") {
    // unit gain
    actuator->gainprm[0] = 1;

    // implied parameters
    actuator->dyntype = mjDYN_NONE;
    actuator->gaintype = mjGAIN_FIXED;
    actuator->biastype = mjBIAS_NONE;
  }

  // position or integrated velocity servo
  else if (type=="position" || type=="intvelocity") {
    // explicit attributes
    ReadAttr(elem, "kp", 1, actuator->gainprm, text);
    actuator->biasprm[1] = -actuator->gainprm[0];

    // read kv
    double kv = -1;  // -1: undefined
    if (ReadAttr(elem, "kv", 1, &kv, text)) {
      if (kv < 0) throw mjXError(elem, "kv cannot be negative");
    }

    // read dampratio
    double dampratio = -1;  // -1: undefined
    if (ReadAttr(elem, "dampratio", 1, &dampratio, text)) {
      if (dampratio < 0) throw mjXError(elem, "dampratio cannot be negative");
    }

    // set biasprm[2]; negative: regular damping, positive: dampratio
    if (dampratio > 0 && kv > 0) {
      throw mjXError(elem, "kv and dampratio cannot both be defined");
    }
    if (kv > 0) actuator->biasprm[2] = -kv;
    if (dampratio > 0) actuator->biasprm[2] = dampratio;

    // read timeconst, set dyntype
    if (ReadAttr(elem, "timeconst", 1, actuator->dynprm, text)) {
      if (actuator->dynprm[0] < 0)
        throw mjXError(elem, "timeconst cannot be negative");
      actuator->dyntype = actuator->dynprm[0] ? mjDYN_FILTEREXACT : mjDYN_NONE;
    }

    // handle inheritrange
    ReadAttr(elem, "inheritrange", 1, &actuator->inheritrange, text);
    if (actuator->inheritrange > 0) {
      if (type == "position") {
        if (actuator->ctrlrange[0] || actuator->ctrlrange[1]) {
          throw mjXError(elem, "ctrlrange and inheritrange cannot both be defined");
        }
      } else {
        if (actuator->actrange[0] || actuator->actrange[1]) {
          throw mjXError(elem, "actrange and inheritrange cannot both be defined");
        }
      }
    }

    // implied parameters
    actuator->gaintype = mjGAIN_FIXED;
    actuator->biastype = mjBIAS_AFFINE;

    if (type=="intvelocity") {
      actuator->dyntype = mjDYN_INTEGRATOR;
      actuator->actlimited = 1;
    }
  }

  // velocity servo
  else if (type=="velocity") {
    // clear bias
    mjuu_zerovec(actuator->biasprm, mjNBIAS);

    // explicit attributes
    ReadAttr(elem, "kv", 1, actuator->gainprm, text);
    actuator->biasprm[2] = -actuator->gainprm[0];

    // implied parameters
    actuator->dyntype = mjDYN_NONE;
    actuator->gaintype = mjGAIN_FIXED;
    actuator->biastype = mjBIAS_AFFINE;
  }

  // damper
  else if (type=="damper") {
    // clear gain
    mjuu_zerovec(actuator->gainprm, mjNGAIN);

    // explicit attributes
    ReadAttr(elem, "kv", 1, actuator->gainprm+2, text);
    if (actuator->gainprm[2]<0)
      throw mjXError(elem, "damping coefficient cannot be negative");
    actuator->gainprm[2] = -actuator->gainprm[2];

    // require nonnegative range
    if (actuator->ctrlrange[0]<0 || actuator->ctrlrange[1]<0) {
      throw mjXError(elem, "damper control range cannot be negative");
    }

    // implied parameters
    actuator->ctrllimited = 1;
    actuator->dyntype = mjDYN_NONE;
    actuator->gaintype = mjGAIN_AFFINE;
    actuator->biastype = mjBIAS_NONE;
  }

  // cylinder
  else if (type=="cylinder") {
    // explicit attributes
    ReadAttr(elem, "timeconst", 1, actuator->dynprm, text);
    ReadAttr(elem, "bias", 3, actuator->biasprm, text);
    ReadAttr(elem, "area", 1, actuator->gainprm, text);
    double diameter;
    if (ReadAttr(elem, "diameter", 1, &diameter, text)) {
      actuator->gainprm[0] = mjPI / 4 * diameter*diameter;
    }

    // implied parameters
    actuator->dyntype = mjDYN_FILTER;
    actuator->gaintype = mjGAIN_FIXED;
    actuator->biastype = mjBIAS_AFFINE;
  }

  // muscle
  else if (type=="muscle") {
    // set muscle defaults if same as global defaults
    if (actuator->dynprm[0]==1) actuator->dynprm[0] = 0.01;    // tau act
    if (actuator->dynprm[1]==0) actuator->dynprm[1] = 0.04;    // tau deact
    if (actuator->gainprm[0]==1) actuator->gainprm[0] = 0.75;  // range[0]
    if (actuator->gainprm[1]==0) actuator->gainprm[1] = 1.05;  // range[1]
    if (actuator->gainprm[2]==0) actuator->gainprm[2] = -1;    // force
    if (actuator->gainprm[3]==0) actuator->gainprm[3] = 200;   // scale
    if (actuator->gainprm[4]==0) actuator->gainprm[4] = 0.5;   // lmin
    if (actuator->gainprm[5]==0) actuator->gainprm[5] = 1.6;   // lmax
    if (actuator->gainprm[6]==0) actuator->gainprm[6] = 1.5;   // vmax
    if (actuator->gainprm[7]==0) actuator->gainprm[7] = 1.3;   // fpmax
    if (actuator->gainprm[8]==0) actuator->gainprm[8] = 1.2;   // fvmax

    // explicit attributes
    ReadAttr(elem, "timeconst", 2, actuator->dynprm, text);
    ReadAttr(elem, "tausmooth", 1, actuator->dynprm+2, text);
    if (actuator->dynprm[2]<0)
      throw mjXError(elem, "muscle tausmooth cannot be negative");
    ReadAttr(elem, "range", 2, actuator->gainprm, text);
    ReadAttr(elem, "force", 1, actuator->gainprm+2, text);
    ReadAttr(elem, "scale", 1, actuator->gainprm+3, text);
    ReadAttr(elem, "lmin", 1, actuator->gainprm+4, text);
    ReadAttr(elem, "lmax", 1, actuator->gainprm+5, text);
    ReadAttr(elem, "vmax", 1, actuator->gainprm+6, text);
    ReadAttr(elem, "fpmax", 1, actuator->gainprm+7, text);
    ReadAttr(elem, "fvmax", 1, actuator->gainprm+8, text);

    // biasprm = gainprm
    for (int n=0; n<9; n++) {
      actuator->biasprm[n] = actuator->gainprm[n];
    }

    // implied parameters
    actuator->dyntype = mjDYN_MUSCLE;
    actuator->gaintype = mjGAIN_MUSCLE;
    actuator->biastype = mjBIAS_MUSCLE;
  }

  // adhesion
  else if (type=="adhesion") {
    // explicit attributes
    ReadAttr(elem, "gain", 1, actuator->gainprm, text);
    if (actuator->gainprm[0]<0)
      throw mjXError(elem, "adhesion gain cannot be negative");

    // require nonnegative range
    ReadAttr(elem, "ctrlrange", 2, actuator->ctrlrange, text);
    if (actuator->ctrlrange[0]<0 || actuator->ctrlrange[1]<0) {
      throw mjXError(elem, "adhesion control range cannot be negative");
    }

    // implied parameters
    actuator->ctrllimited = 1;
    actuator->gaintype = mjGAIN_FIXED;
    actuator->biastype = mjBIAS_NONE;
  }

  else if (type == "plugin") {
    OnePlugin(elem, &actuator->plugin);
    int n;
    if (MapValue(elem, "dyntype", &n, dyn_map, dyn_sz)) {
      actuator->dyntype = (mjtDyn)n;
    }
    if (MapValue(elem, "actearly", &n, bool_map, 2)) {
      actuator->actearly = (n==1);
    }
    ReadAttr(elem, "dynprm", mjNDYN, actuator->dynprm, text, false, false);
    ReadAttrInt(elem, "actdim", &actuator->actdim);
  }

  else {          // SHOULD NOT OCCUR
    throw mjXError(elem, "unrecognized actuator type: %s", type.c_str());
  }

  // read userdata
  std::vector<double> userdata;
  if (ReadVector(elem, "user", userdata, text)) {
    mjs_setDouble(actuator->userdata, userdata.data(), userdata.size());
  }

  // write info
  mjs_setString(actuator->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
}



// make composite
void mjXReader::OneComposite(XMLElement* elem, mjsBody* body, mjsDefault* def) {
  string text;
  int n;

  // create out-of-DOM element
  mjCComposite comp;

  // common properties
  ReadAttrTxt(elem, "prefix", comp.prefix);
  if (MapValue(elem, "type", &n, comp_map, mjNCOMPTYPES, true)) {
    comp.type = (mjtCompType)n;
  }
  ReadAttr(elem, "count", 3, comp.count, text, false, false);
  ReadAttr(elem, "spacing", 1, &comp.spacing, text, false);
  ReadAttr(elem, "offset", 3, comp.offset, text);
  ReadAttr(elem, "flatinertia", 1, &comp.flatinertia, text);

  // plugin
  XMLElement* eplugin = FirstChildElement(elem, "plugin");
  if (eplugin) {
    OnePlugin(eplugin, &comp.plugin);
  }

  // cable
  string curves;
  ReadAttrTxt(elem, "curve", curves);
  ReadAttrTxt(elem, "initial", comp.initial);
  ReadAttr(elem, "size", 3, comp.size, text, false, false);
  auto uservert = ReadAttrVec<float>(elem, "vertex");
  if (uservert.has_value()) {
    comp.uservert = std::move(uservert.value());
  }

  // shell
  ReadAttrTxt(elem, "face", comp.userface);

  // process curve string
  std::istringstream iss(curves);
  int i = 0;
  while (iss) {
    iss >> text;
    if (i>2) {
      throw mjXError(elem, "The curve array must have a maximum of 3 components");
    }
    comp.curve[i++] = (mjtCompShape)FindKey(shape_map, mjNCOMPSHAPES, text);
    if (iss.eof()){
      break;
    }
  };

  // skin
  XMLElement* eskin = FirstChildElement(elem, "skin");
  if (eskin) {
    comp.skin = true;
    if (MapValue(eskin, "texcoord", &n, bool_map, 2)) {
      comp.skintexcoord = (n==1);
    }
    ReadAttrTxt(eskin, "material", comp.skinmaterial);
    ReadAttr(eskin, "rgba", 4, comp.skinrgba, text);
    ReadAttr(eskin, "inflate", 1, &comp.skininflate, text);
    ReadAttrInt(eskin, "subgrid", &comp.skinsubgrid);
    ReadAttrInt(eskin, "group", &comp.skingroup, 0);
    if (comp.skingroup<0 || comp.skingroup>=mjNGROUP) {
      throw mjXError(eskin, "skin group must be between 0 and 5");
    }
  }

  // set type-specific defaults
  comp.SetDefault();

  // parse smooth solver parameters after type-specific defaults are set
  ReadAttr(elem, "solrefsmooth", mjNREF, comp.solrefsmooth, text, false, false);
  ReadAttr(elem, "solimpsmooth", mjNIMP, comp.solimpsmooth, text, false, false);

  // geom
  XMLElement* egeom = FirstChildElement(elem, "geom");
  if (egeom) {
    string material;
    mjsGeom& dgeom = *comp.def[0].spec.geom;
    if (MapValue(egeom, "type", &n, geom_map, mjNGEOMTYPES)) {
      dgeom.type = (mjtGeom)n;
    }
    ReadAttr(egeom, "size", 3, dgeom.size, text, false, false);
    ReadAttrInt(egeom, "contype", &dgeom.contype);
    ReadAttrInt(egeom, "conaffinity", &dgeom.conaffinity);
    ReadAttrInt(egeom, "condim", &dgeom.condim);
    ReadAttrInt(egeom, "group", &dgeom.group);
    ReadAttrInt(egeom, "priority", &dgeom.priority);
    ReadAttr(egeom, "friction", 3, dgeom.friction, text, false, false);
    ReadAttr(egeom, "solmix", 1, &dgeom.solmix, text);
    ReadAttr(egeom, "solref", mjNREF, dgeom.solref, text, false, false);
    ReadAttr(egeom, "solimp", mjNIMP, dgeom.solimp, text, false, false);
    ReadAttr(egeom, "margin", 1, &dgeom.margin, text);
    ReadAttr(egeom, "gap", 1, &dgeom.gap, text);
    if (ReadAttrTxt(egeom, "material", material)) {
      mjs_setString(dgeom.material, material.c_str());
    }
    ReadAttr(egeom, "rgba", 4, dgeom.rgba, text);
    ReadAttr(egeom, "mass", 1, &dgeom.mass, text);
    ReadAttr(egeom, "density", 1, &dgeom.density, text);
  }

  // site
  XMLElement* esite = FirstChildElement(elem, "site");
  if (esite) {
    string material;
    mjsSite& dsite = *comp.def[0].spec.site;
    ReadAttr(esite, "size", 3, dsite.size, text, false, false);
    ReadAttrInt(esite, "group", &dsite.group);
    ReadAttrTxt(esite, "material", material);
    ReadAttr(esite, "rgba", 4, dsite.rgba, text);
    mjs_setString(dsite.material, material.c_str());
  }

  // joint
  XMLElement* ejnt = FirstChildElement(elem, "joint");
  while (ejnt) {
    // kind
    int kind;
    MapValue(ejnt, "kind", &kind, jkind_map, 4, true);

    // create a new element if this kind already exists
    if (comp.add[kind]) {
      char error[200];
      if (!comp.AddDefaultJoint(error, 200)) {
        throw mjXError(elem, "%s", error);
      }
    }
    comp.add[kind] = true;

    // get element
    mjsDefault* dspec = &comp.defjoint[(mjtCompKind)kind].back().spec;
    mjsJoint& djoint = *dspec->joint;
    mjsEquality& dequality = *dspec->equality;

    // particle joint
    if (MapValue(ejnt, "type", &n, joint_map, joint_sz)) {
      djoint.type = (mjtJoint)n;
    }
    ReadAttr(ejnt, "axis", 3, djoint.axis, text);

    // solreffix, solimpfix
    ReadAttr(ejnt, "solreffix", mjNREF, dequality.solref, text, false, false);
    ReadAttr(ejnt, "solimpfix", mjNIMP, dequality.solimp, text, false, false);

    // joint attributes
    MapValue(elem, "limited", &djoint.limited, TFAuto_map, 3);
    ReadAttrInt(ejnt, "group", &djoint.group);
    ReadAttr(ejnt, "solreflimit", mjNREF, djoint.solref_limit, text, false, false);
    ReadAttr(ejnt, "solimplimit", mjNIMP, djoint.solimp_limit, text, false, false);
    ReadAttr(ejnt,
             "solreffriction", mjNREF, djoint.solref_friction, text, false, false);
    ReadAttr(ejnt,
             "solimpfriction", mjNIMP, djoint.solimp_friction, text, false, false);
    ReadAttr(ejnt, "stiffness", 1, &djoint.stiffness, text);
    ReadAttr(ejnt, "range", 2, djoint.range, text);
    ReadAttr(ejnt, "margin", 1, &djoint.margin, text);
    ReadAttr(ejnt, "armature", 1, &djoint.armature, text);
    ReadAttr(ejnt, "damping", 1, &djoint.damping, text);
    ReadAttr(ejnt, "frictionloss", 1, &djoint.frictionloss, text);

    // advance
    ejnt = NextSiblingElement(ejnt, "joint");
  }

  // tendon
  XMLElement* eten = FirstChildElement(elem, "tendon");
  while (eten) {
    // kind
    int kind;
    MapValue(eten, "kind", &kind, tkind_map, 2, true);
    comp.add[kind] = true;

    // get default structs
    mjsTendon& dtendon = *comp.def[kind].spec.tendon;
    mjsEquality& dequality = *comp.def[kind].spec.equality;

    // solreffix, solimpfix
    ReadAttr(eten, "solreffix", mjNREF, dequality.solref, text, false, false);
    ReadAttr(eten, "solimpfix", mjNIMP, dequality.solimp, text, false, false);

    // tendon attributes
    string material;
    MapValue(elem, "limited", &dtendon.limited, TFAuto_map, 3);
    ReadAttrInt(eten, "group", &dtendon.group);
    ReadAttr(eten, "solreflimit", mjNREF, dtendon.solref_limit, text, false, false);
    ReadAttr(eten, "solimplimit", mjNIMP, dtendon.solimp_limit, text, false, false);
    ReadAttr(eten,
             "solreffriction", mjNREF, dtendon.solref_friction, text, false, false);
    ReadAttr(eten,
             "solimpfriction", mjNIMP, dtendon.solimp_friction, text, false, false);
    ReadAttr(eten, "range", 2, dtendon.range, text);
    ReadAttr(eten, "margin", 1, &dtendon.margin, text);
    ReadAttr(eten, "stiffness", 1, &dtendon.stiffness, text);
    ReadAttr(eten, "damping", 1, &dtendon.damping, text);
    ReadAttr(eten, "frictionloss", 1, &dtendon.frictionloss, text);
    ReadAttrTxt(eten, "material", material);
    mjs_setString(dtendon.material, material.c_str());
    ReadAttr(eten, "rgba", 4, dtendon.rgba, text);
    ReadAttr(eten, "width", 1, &dtendon.width, text);

    // advance
    eten = NextSiblingElement(eten, "tendon");
  }

  // pin
  XMLElement* epin = FirstChildElement(elem, "pin");
  while (epin) {
    // read
    int coord[2] = {0, 0};
    ReadAttr(epin, "coord", 2, coord, text, true, false);

    // insert 2 coordinates (2nd may be unused)
    comp.pin.push_back(coord[0]);
    comp.pin.push_back(coord[1]);

    // advance
    epin = NextSiblingElement(epin, "pin");
  }

  // make composite
  char error[200];
  bool res = comp.Make(spec, body, error, 200);

  // throw error
  if (!res) {
    throw mjXError(elem, "%s", error);
  }
}



// make flexcomp
void mjXReader::OneFlexcomp(XMLElement* elem, mjsBody* body, const mjVFS* vfs) {
  string text, material;
  int n;

  // create out-of-DOM element
  mjCFlexcomp fcomp;
  mjsFlex& dflex = *fcomp.def.spec.flex;

  // common properties
  ReadAttrTxt(elem, "name", fcomp.name, true);
  if (MapValue(elem, "type", &n, fcomp_map, mjNFCOMPTYPES)) {
    fcomp.type = (mjtFcompType)n;
  }
  ReadAttr(elem, "count", 3, fcomp.count, text);
  ReadAttr(elem, "spacing", 3, fcomp.spacing, text);
  ReadAttr(elem, "scale", 3, fcomp.scale, text);
  ReadAttr(elem, "mass", 1, &fcomp.mass, text);
  ReadAttr(elem, "inertiabox", 1, &fcomp.inertiabox, text);
  auto maybe_file = ReadAttrFile(elem, "file", vfs, modelfiledir_);
  if (maybe_file.has_value()) {
    fcomp.file = std::move(maybe_file.value().Str());
  } else {
    fcomp.file = "";
  }
  if (ReadAttrTxt(elem, "material", material)) {
    mjs_setString(dflex.material, material.c_str());
  }
  ReadAttr(elem, "rgba", 4, dflex.rgba, text);
  if (MapValue(elem, "flatskin", &n, bool_map, 2)) {
    dflex.flatskin = (n==1);
  }
  ReadAttrInt(elem, "dim", &dflex.dim);
  ReadAttr(elem, "radius", 1, &dflex.radius, text);
  ReadAttrInt(elem, "group", &dflex.group);

  // pose
  ReadAttr(elem, "pos", 3, fcomp.pos, text);
  ReadAttr(elem, "quat", 4, fcomp.quat, text);
  ReadAlternative(elem, fcomp.alt);

  // user or internal
  if (MapValue(elem, "rigid", &n, bool_map, 2)) {
    fcomp.rigid = (n==1);
  }
  auto point = ReadAttrVec<double>(elem, "point");
  if (point.has_value()) {
    fcomp.point = std::move(point.value());
  }
  auto element = ReadAttrVec<int>(elem, "element");
  if (element.has_value()) {
    fcomp.element = std::move(element.value());
  }
  auto texcoord = ReadAttrVec<float>(elem, "texcoord");
  if (texcoord.has_value()) {
    fcomp.texcoord = std::move(texcoord.value());
  }

  // edge
  XMLElement* edge = FirstChildElement(elem, "edge");
  if (edge) {
    if (MapValue(edge, "equality", &n, bool_map, 2)) {
      fcomp.equality = (n==1);
    }
    ReadAttr(edge, "solref", mjNREF, fcomp.def.spec.equality->solref, text, false, false);
    ReadAttr(edge, "solimp", mjNIMP, fcomp.def.spec.equality->solimp, text, false, false);
    ReadAttr(edge, "stiffness", 1, &dflex.edgestiffness, text);
    ReadAttr(edge, "damping", 1, &dflex.edgedamping, text);
  }

  // contact
  XMLElement* cont = FirstChildElement(elem, "contact");
  if (cont) {
    ReadAttrInt(cont, "contype", &dflex.contype);
    ReadAttrInt(cont, "conaffinity", &dflex.conaffinity);
    ReadAttrInt(cont, "condim", &dflex.condim);
    ReadAttrInt(cont, "priority", &dflex.priority);
    ReadAttr(cont, "friction", 3, dflex.friction, text, false, false);
    ReadAttr(cont, "solmix", 1, &dflex.solmix, text);
    ReadAttr(cont, "solref", mjNREF, dflex.solref, text, false, false);
    ReadAttr(cont, "solimp", mjNIMP, dflex.solimp, text, false, false);
    ReadAttr(cont, "margin", 1, &dflex.margin, text);
    ReadAttr(cont, "gap", 1, &dflex.gap, text);
    if (MapValue(cont, "internal", &n, bool_map, 2)) {
      dflex.internal = (n==1);
    }
    MapValue(cont, "selfcollide", &dflex.selfcollide, flexself_map, 5);
    ReadAttrInt(cont, "activelayers", &dflex.activelayers);
  }

  // pin
  XMLElement* epin = FirstChildElement(elem, "pin");
  while (epin) {
    auto id = ReadAttrVec<int>(epin, "id");
    if (id.has_value()) {
      fcomp.pinid.insert(fcomp.pinid.end(), id->begin(), id->end());
    }
    auto range = ReadAttrVec<int>(epin, "range");
    if (range.has_value()) {
      fcomp.pinrange.insert(fcomp.pinrange.end(), range->begin(), range->end());
    }
    auto grid = ReadAttrVec<int>(epin, "grid");
    if (grid.has_value()) {
      fcomp.pingrid.insert(fcomp.pingrid.end(), grid->begin(), grid->end());
    }
    auto gridrange = ReadAttrVec<int>(epin, "gridrange");
    if (gridrange.has_value()) {
      fcomp.pingridrange.insert(fcomp.pingridrange.end(),
                                gridrange->begin(), gridrange->end());
    }

    // advance
    epin = NextSiblingElement(epin, "pin");
  }

  // plugin
  XMLElement* eplugin = FirstChildElement(elem, "plugin");
  if (eplugin) {
    OnePlugin(eplugin, &fcomp.plugin);
  }

  // make flexcomp
  char error[200];
  bool res = fcomp.Make(spec, body, error, 200);

  // throw error
  if (!res) {
    throw mjXError(elem, "%s", error);
  }
}



// add plugin
void mjXReader::OnePlugin(XMLElement* elem, mjsPlugin* plugin) {
  plugin->active = true;
  string name = "";
  string instance_name = "";
  ReadAttrTxt(elem, "plugin", name);
  ReadAttrTxt(elem, "instance", instance_name);
  mjs_setString(plugin->name, name.c_str());
  mjs_setString(plugin->instance_name, instance_name.c_str());
  if (instance_name.empty()) {
    plugin->instance = mjs_addPlugin(spec)->instance;
    ReadPluginConfigs(elem, plugin);
  } else {
    spec->hasImplicitPluginElem = true;
  }
}



//------------------ MJCF-specific sections --------------------------------------------------------

// default section parser
void mjXReader::Default(XMLElement* section, const mjsDefault* def, const mjVFS* vfs) {
  XMLElement* elem;
  string text, name;

  // create new default, except at top level (already added in mjCModel constructor)
  text.clear();
  ReadAttrTxt(section, "class", text);
  if (text.empty()) {
    if (def) {
      throw mjXError(section, "empty class name");
    }
  }
  if (def) {
    def = mjs_addDefault(spec, text.c_str(), def);
    if (!def) {
      throw mjXError(section, "repeated default class name");
    }
  } else {
    def = mjs_getSpecDefault(spec);
    if (!text.empty() && text != "main") {
      throw mjXError(section, "top-level default class 'main' cannot be renamed");
    }
  }

  // iterate over elements other than nested defaults
  elem = FirstChildElement(section);
  while (elem) {
    // get element name
    name = elem->Value();

    // read mesh
    if (name=="mesh") OneMesh(elem, def->mesh, vfs);

    // read material
    else if (name=="material") OneMaterial(elem, def->material);

    // read joint
    else if (name=="joint") OneJoint(elem, def->joint);

    // read geom
    else if (name=="geom") OneGeom(elem, def->geom);

    // read site
    else if (name=="site") OneSite(elem, def->site);

    // read camera
    else if (name=="camera") OneCamera(elem, def->camera);

    // read light
    else if (name=="light") OneLight(elem, def->light);

    // read pair
    else if (name=="pair") OnePair(elem, def->pair);

    // read equality
    else if (name=="equality") OneEquality(elem, def->equality);

    // read tendon
    else if (name=="tendon") OneTendon(elem, def->tendon);

    // read actuator
    else if (name=="general"     ||
             name=="motor"       ||
             name=="position"    ||
             name=="velocity"    ||
             name=="damper"      ||
             name=="intvelocity" ||
             name=="cylinder"    ||
             name=="muscle"      ||
             name=="adhesion") {
      OneActuator(elem, def->actuator);
    }

    // advance
    elem = NextSiblingElement(elem);
  }

  // iterate over nested defaults
  elem = FirstChildElement(section);
  while (elem) {
    // get element name
    name = elem->Value();

    // read default
    if (name=="default") {
      Default(elem, def, vfs);
    }

    // advance
    elem = NextSiblingElement(elem);
  }
}



// extension section parser
void mjXReader::Extension(XMLElement* section) {
  XMLElement* elem = FirstChildElement(section);
  std::vector<std::pair<const mjpPlugin*, int>> active_plugins;

  while (elem) {
    // get sub-element name
    string_view name = elem->Value();

    if (name == "plugin") {
      string plugin_name;
      int plugin_slot = -1;
      ReadAttrTxt(elem, "plugin", plugin_name, /* required = */ true);
      const mjpPlugin* plugin = mjp_getPlugin(plugin_name.c_str(), &plugin_slot);
      if (!plugin) {
        throw mjXError(elem, "unknown plugin '%s'", plugin_name.c_str());
      }

      bool already_declared = false;
      for (const auto& [existing_plugin, existing_slot] : active_plugins) {
        if (plugin == existing_plugin) {
          already_declared = true;
          break;
        }
      }
      if (!already_declared) {
        active_plugins.emplace_back(std::make_pair(plugin, plugin_slot));
      }

      XMLElement* child = FirstChildElement(elem);
      while (child) {
        if (string(child->Value())=="instance") {
          if (spec->hasImplicitPluginElem) {
            throw mjXError(
                child, "explicit plugin instance must appear before implicit plugin elements");
          }
          string name;
          mjsPlugin* p = mjs_addPlugin(spec);
          mjs_setString(p->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
          ReadAttrTxt(child, "name", name, /* required = */ true);
          mjs_setString(p->name, name.c_str());
          if (!p->name) {
            throw mjXError(child, "plugin instance must have a name");
          }
          ReadPluginConfigs(child, p);
          p->plugin_slot = plugin_slot;
        }
        child = NextSiblingElement(child);
      }
    }

    // advance to next element
    elem = NextSiblingElement(elem);
  }

  mjs_setActivePlugins(spec, &active_plugins);
}



// custom section parser
void mjXReader::Custom(XMLElement* section) {
  string str, name;
  XMLElement* elem;
  double data[500];

  // iterate over child elements
  elem = FirstChildElement(section);
  while (elem) {
    // get sub-element name
    name = elem->Value();
    string elname;

    // numeric
    if (name=="numeric") {
      // create custom
      mjsNumeric* numeric = mjs_addNumeric(spec);

      // write error info
      mjs_setString(numeric->info, ("line " + std::to_string(elem->GetLineNum())).c_str());

      // read attributes
      ReadAttrTxt(elem, "name", elname, true);
      mjs_setString(numeric->name, elname.c_str());
      if (ReadAttrInt(elem, "size", &numeric->size)) {
        int sz = numeric->size < 500 ? numeric->size : 500;
        for (int i=0; i<sz; i++) {
          data[i] = 0;
        }
      } else {
        numeric->size = 501;
      }
      int len = ReadAttr(elem, "data", numeric->size, data, str, false, false);
      if (numeric->size==501) {
        numeric->size = len;
      }
      if (numeric->size<1 || numeric->size>500) {
        throw mjXError(elem, "custom field size must be between 1 and 500");
      }

      // copy data
      mjs_setDouble(numeric->data, data, numeric->size);
    }

    // text
    else if (name=="text") {
      // create custom
      mjsText* text = mjs_addText(spec);

      // write error info
      mjs_setString(text->info, ("line " + std::to_string(elem->GetLineNum())).c_str());

      // read attributes
      ReadAttrTxt(elem, "name", elname, true);
      mjs_setString(text->name, elname.c_str());
      ReadAttrTxt(elem, "data", str, true);
      if (str.empty()) {
        throw mjXError(elem, "text field cannot be empty");
      }

      // copy data
      mjs_setString(text->data, str.c_str());
    }

    // tuple
    else if (name=="tuple") {
      // create custom
      mjsTuple* tuple = mjs_addTuple(spec);

      // write error info
      mjs_setString(tuple->info, ("line " + std::to_string(elem->GetLineNum())).c_str());

      // read attributes
      ReadAttrTxt(elem, "name", elname, true);
      mjs_setString(tuple->name, elname.c_str());

      // read objects and add
      XMLElement* obj = FirstChildElement(elem);
      std::vector<int> objtype;
      string objname = "";
      std::vector<double> objprm;

      while (obj) {
        // get sub-element name
        name = obj->Value();

        // new object
        if (name=="element") {
          // read type, check and assign
          ReadAttrTxt(obj, "objtype", str, true);
          mjtObj otype = (mjtObj)mju_str2Type(str.c_str());
          if (otype==mjOBJ_UNKNOWN) {
            throw mjXError(obj, "unknown object type");
          }
          objtype.push_back(otype);

          // read name and assign
          ReadAttrTxt(obj, "objname", str, true);
          objname += " " + str;

          // read parameter and assign
          double oprm = 0;
          ReadAttr(obj, "prm", 1, &oprm, str);
          objprm.push_back(oprm);
        }

        // advance to next object
        obj = NextSiblingElement(obj);
      }

      mjs_setInt(tuple->objtype, objtype.data(), objtype.size());
      mjs_setStringVec(tuple->objname, objname.c_str());
      mjs_setDouble(tuple->objprm, objprm.data(), objprm.size());
    }

    // advance to next element
    elem = NextSiblingElement(elem);
  }
}



// visual section parser
void mjXReader::Visual(XMLElement* section) {
  string text, name;
  XMLElement* elem;
  mjVisual* vis = &spec->visual;
  int n;

  // iterate over child elements
  elem = FirstChildElement(section);
  while (elem) {
    // get sub-element name
    name = elem->Value();

    // global sub-element
    if (name=="global") {
      if (MapValue(elem, "orthographic", &n, bool_map, 2)) {
        vis->global.orthographic = (n==1);
      }
      ReadAttr(elem,    "fovy",      1, &vis->global.fovy,      text);
      ReadAttr(elem,    "ipd",       1, &vis->global.ipd,       text);
      ReadAttr(elem,    "azimuth",   1, &vis->global.azimuth,   text);
      ReadAttr(elem,    "elevation", 1, &vis->global.elevation, text);
      ReadAttr(elem,    "linewidth", 1, &vis->global.linewidth, text);
      ReadAttr(elem,    "glow",      1, &vis->global.glow,      text);
      ReadAttrInt(elem, "offwidth",     &vis->global.offwidth);
      ReadAttrInt(elem, "offheight",    &vis->global.offheight);
      if (ReadAttr(elem, "realtime", 1, &vis->global.realtime, text)) {
        if (vis->global.realtime<=0) {
          throw mjXError(elem, "realtime must be greater than 0");
        }
      }
      if (MapValue(elem, "ellipsoidinertia", &n, bool_map, 2)) {
        vis->global.ellipsoidinertia = (n==1);
      }
      if (MapValue(elem, "bvactive", &n, bool_map, 2)) {
        vis->global.bvactive = (n==1);
      }
    }

    // quality sub-element
    else if (name=="quality") {
      ReadAttrInt(elem, "shadowsize", &vis->quality.shadowsize);
      ReadAttrInt(elem, "offsamples", &vis->quality.offsamples);
      ReadAttrInt(elem, "numslices",  &vis->quality.numslices);
      ReadAttrInt(elem, "numstacks",  &vis->quality.numstacks);
      ReadAttrInt(elem, "numquads",   &vis->quality.numquads);
    }

    // headlight sub-element
    else if (name=="headlight") {
      ReadAttr(elem, "ambient",  3, vis->headlight.ambient,  text);
      ReadAttr(elem, "diffuse",  3, vis->headlight.diffuse,  text);
      ReadAttr(elem, "specular", 3, vis->headlight.specular, text);
      ReadAttrInt(elem, "active",  &vis->headlight.active);
    }

    // map sub-element
    else if (name=="map") {
      ReadAttr(elem, "stiffness",      1, &vis->map.stiffness, text);
      ReadAttr(elem, "stiffnessrot",   1, &vis->map.stiffnessrot, text);
      ReadAttr(elem, "force",          1, &vis->map.force,     text);
      ReadAttr(elem, "torque",         1, &vis->map.torque,    text);
      ReadAttr(elem, "alpha",          1, &vis->map.alpha,     text);
      ReadAttr(elem, "fogstart",       1, &vis->map.fogstart,  text);
      ReadAttr(elem, "fogend",         1, &vis->map.fogend,    text);
      ReadAttr(elem, "znear",          1, &vis->map.znear,     text);
      if (vis->map.znear<=0) {
        throw mjXError(elem, "znear must be strictly positive");
      }
      ReadAttr(elem, "zfar",           1, &vis->map.zfar,      text);
      ReadAttr(elem, "haze",           1, &vis->map.haze,      text);
      ReadAttr(elem, "shadowclip",     1, &vis->map.shadowclip, text);
      ReadAttr(elem, "shadowscale",    1, &vis->map.shadowscale, text);
      ReadAttr(elem, "actuatortendon", 1, &vis->map.actuatortendon, text);
    }

    // scale sub-element
    else if (name=="scale") {
      ReadAttr(elem, "forcewidth",     1, &vis->scale.forcewidth,     text);
      ReadAttr(elem, "contactwidth",   1, &vis->scale.contactwidth,   text);
      ReadAttr(elem, "contactheight",  1, &vis->scale.contactheight,  text);
      ReadAttr(elem, "connect",        1, &vis->scale.connect,        text);
      ReadAttr(elem, "com",            1, &vis->scale.com,            text);
      ReadAttr(elem, "camera",         1, &vis->scale.camera,         text);
      ReadAttr(elem, "light",          1, &vis->scale.light,          text);
      ReadAttr(elem, "selectpoint",    1, &vis->scale.selectpoint,    text);
      ReadAttr(elem, "jointlength",    1, &vis->scale.jointlength,    text);
      ReadAttr(elem, "jointwidth",     1, &vis->scale.jointwidth,     text);
      ReadAttr(elem, "actuatorlength", 1, &vis->scale.actuatorlength, text);
      ReadAttr(elem, "actuatorwidth",  1, &vis->scale.actuatorwidth,  text);
      ReadAttr(elem, "framelength",    1, &vis->scale.framelength,    text);
      ReadAttr(elem, "framewidth",     1, &vis->scale.framewidth,     text);
      ReadAttr(elem, "constraint",     1, &vis->scale.constraint,     text);
      ReadAttr(elem, "slidercrank",    1, &vis->scale.slidercrank,    text);
      ReadAttr(elem, "frustum",        1, &vis->scale.frustum,        text);
    }

    // rgba sub-element
    else if (name=="rgba") {
      ReadAttr(elem, "fog",              4, vis->rgba.fog,             text);
      ReadAttr(elem, "haze",             4, vis->rgba.haze,            text);
      ReadAttr(elem, "force",            4, vis->rgba.force,           text);
      ReadAttr(elem, "inertia",          4, vis->rgba.inertia,         text);
      ReadAttr(elem, "joint",            4, vis->rgba.joint,           text);
      ReadAttr(elem, "actuator",         4, vis->rgba.actuator,        text);
      ReadAttr(elem, "actuatornegative", 4, vis->rgba.actuatornegative, text);
      ReadAttr(elem, "actuatorpositive", 4, vis->rgba.actuatorpositive, text);
      ReadAttr(elem, "com",              4, vis->rgba.com,             text);
      ReadAttr(elem, "camera",           4, vis->rgba.camera,          text);
      ReadAttr(elem, "light",            4, vis->rgba.light,           text);
      ReadAttr(elem, "selectpoint",      4, vis->rgba.selectpoint,     text);
      ReadAttr(elem, "connect",          4, vis->rgba.connect,         text);
      ReadAttr(elem, "contactpoint",     4, vis->rgba.contactpoint,    text);
      ReadAttr(elem, "contactforce",     4, vis->rgba.contactforce,    text);
      ReadAttr(elem, "contactfriction",  4, vis->rgba.contactfriction, text);
      ReadAttr(elem, "contacttorque",    4, vis->rgba.contacttorque,   text);
      ReadAttr(elem, "contactgap",       4, vis->rgba.contactgap,      text);
      ReadAttr(elem, "rangefinder",      4, vis->rgba.rangefinder,     text);
      ReadAttr(elem, "constraint",       4, vis->rgba.constraint,      text);
      ReadAttr(elem, "slidercrank",      4, vis->rgba.slidercrank,     text);
      ReadAttr(elem, "crankbroken",      4, vis->rgba.crankbroken,     text);
      ReadAttr(elem, "frustum",          4, vis->rgba.frustum,         text);
      ReadAttr(elem, "bv",               4, vis->rgba.bv,              text);
      ReadAttr(elem, "bvactive",         4, vis->rgba.bvactive,        text);
    }

    // advance to next element
    elem = NextSiblingElement(elem);
  }
}



// asset section parser
void mjXReader::Asset(XMLElement* section, const mjVFS* vfs) {
  int n;
  string text, name, texname, content_type;
  XMLElement* elem;

  // iterate over child elements
  elem = FirstChildElement(section);
  while (elem) {
    // get sub-element name
    name = elem->Value();

    // get class if specified, otherwise use default0
    mjsDefault* def = GetClass(elem);
    if (!def) {
      def = mjs_getSpecDefault(spec);
    }

    // texture sub-element
    if (name=="texture") {
      // create texture
      mjsTexture* texture = mjs_addTexture(spec);

      // write error info
      mjs_setString(texture->info, ("line " + std::to_string(elem->GetLineNum())).c_str());

      // read attributes
      if (MapValue(elem, "type", &n, texture_map, texture_sz)) {
        texture->type = (mjtTexture)n;
      }
      if (ReadAttrTxt(elem, "name", texname)) {
        mjs_setString(texture->name, texname.c_str());
      }
      if (ReadAttrTxt(elem, "content_type", content_type)) {
        mjs_setString(texture->content_type, content_type.c_str());
      }
      auto file = ReadAttrFile(elem, "file", vfs, TextureDir());
      if (file.has_value()) {
        mjs_setString(texture->file, file->c_str());
      }
      ReadAttrInt(elem, "width", &texture->width);
      ReadAttrInt(elem, "height", &texture->height);
      if (!ReadAttrInt(elem, "nchannel", &texture->nchannel)) {
        texture->nchannel = 3;
      }
      ReadAttr(elem, "rgb1", 3, texture->rgb1, text);
      ReadAttr(elem, "rgb2", 3, texture->rgb2, text);
      ReadAttr(elem, "markrgb", 3, texture->markrgb, text);
      ReadAttr(elem, "random", 1, &texture->random, text);
      if (MapValue(elem, "builtin", &n, builtin_map, builtin_sz)) {
        texture->builtin = (mjtBuiltin)n;
      }
      if (MapValue(elem, "mark", &n, mark_map, mark_sz)) {
        texture->mark = (mjtMark)n;
      }
      if (MapValue(elem, "hflip", &n, bool_map, 2)) {
        texture->hflip = (n!=0);
      }
      if (MapValue(elem, "vflip", &n, bool_map, 2)) {
        texture->vflip = (n!=0);
      }

      // grid
      ReadAttr(elem, "gridsize", 2, texture->gridsize, text);
      if (ReadAttrTxt(elem, "gridlayout", text)) {
        // check length
        if (text.length()>12) {
          throw mjXError(elem, "gridlayout length cannot exceed 12 characters");
        }
        if (text.length()!=texture->gridsize[0]*texture->gridsize[1]) {
          throw mjXError(elem, "gridlayout length must match gridsize");
        }

        memcpy(texture->gridlayout, text.data(), text.length());
      }

      // separate files
      std::vector<string> cubefiles(6);
      std::vector<string> cubefile_names = {"fileright", "fileleft",
                                                 "fileup", "filedown",
                                                 "filefront", "fileback"};
      for (int i = 0; i < cubefiles.size(); i++) {
        auto maybe_file = ReadAttrFile(elem, cubefile_names[i].c_str(), vfs,
                                       TextureDir());
        if (maybe_file.has_value()) {
          cubefiles[i] = maybe_file.value().Str();
        } else {
          cubefiles[i] = "";
        }
        mjs_setInStringVec(texture->cubefiles, i, cubefiles[i].c_str());
      }
    }

    // material sub-element
    else if (name=="material") {
      // create material and parse
      mjsMaterial* material = mjs_addMaterial(spec, def);
      OneMaterial(elem, material);
    }

    // mesh sub-element
    else if (name=="mesh") {
      // create mesh and parse
      mjsMesh* mesh = mjs_addMesh(spec, def);
      OneMesh(elem, mesh, vfs);
    }

    // skin sub-element... deprecate ???
    else if (name=="skin") {
      // create skin and parse
      mjsSkin* skin = mjs_addSkin(spec);
      OneSkin(elem, skin, vfs);
    }

    // hfield sub-element
    else if (name=="hfield") {
      // create hfield
      mjsHField* hfield = mjs_addHField(spec);

      // write error info
      mjs_setString(hfield->info, ("line " + std::to_string(elem->GetLineNum())).c_str());

      // read attributes
      string name, content_type;
      if (ReadAttrTxt(elem, "name", name)) {
        mjs_setString(hfield->name, name.c_str());
      }
      if (ReadAttrTxt(elem, "content_type", content_type)) {
        mjs_setString(hfield->content_type, content_type.c_str());
      }
      auto file = ReadAttrFile(elem, "file", vfs, AssetDir());
      if (file.has_value()) {
        mjs_setString(hfield->file, file->c_str());
      }
      ReadAttrInt(elem, "nrow", &hfield->nrow);
      ReadAttrInt(elem, "ncol", &hfield->ncol);
      ReadAttr(elem, "size", 4, hfield->size, text, true);

      // allocate buffer for dynamic hfield, copy user data if given
      if (!file.has_value() && hfield->nrow>0 && hfield->ncol>0) {
        int nrow = hfield->nrow;
        int ncol = hfield->ncol;

        // read user data
        auto userdata = ReadAttrVec<float>(elem, "elevation");

        // user data given, copy into data
        if (userdata.has_value()) {
          if (userdata->size() != nrow*ncol) {
            throw mjXError(elem, "elevation data length must match nrow*ncol");
          }

          // copy in reverse row order, so XML string is top-to-bottom
          std::vector<float> flipped(nrow*ncol);
          for (int i = 0; i < nrow; i++) {
            int flip = nrow-1-i;
            for (int j = 0; j < ncol; j++) {
              flipped[flip*ncol + j] = userdata->data()[i*ncol + j];
            }
          }

          mjs_setFloat(hfield->userdata, flipped.data(), flipped.size());
        }

        // user data not given, set to 0
        else {
          std::vector<float> zero(nrow*ncol);
          mjs_setFloat(hfield->userdata, zero.data(), zero.size());
        }
      }
    }

    // model sub-element
    else if (name=="model") {
      auto filename = modelfiledir_ + ReadAttrFile(elem, "file", vfs).value();

      // parse the child
      std::array<char, 1024> error;
      mjSpec* child = mj_parseXML(filename.c_str(), vfs, error.data(), error.size());
      if (!child) {
        throw mjXError(elem, "could not parse model file with error: %s", error.data());
      }

      // overwrite model name if given
      string modelname = "";
      if (ReadAttrTxt(elem, "name", modelname)) {
        mjs_setString(child->modelname, modelname.c_str());
      }

      // store child spec in model
      mjs_addSpec(spec, child);
    }

    // advance to next element
    elem = NextSiblingElement(elem);
  }
}



// body/world section parser; recursive
void mjXReader::Body(XMLElement* section, mjsBody* body, mjsFrame* frame,
                     const mjVFS* vfs) {
  string text, name;
  XMLElement* elem;
  int n;

  // sanity check
  if (!body) {
    throw mjXError(section, "null body pointer");
  }

  // no attributes allowed in world body
  if (mjs_getId(body->element)==0 && section->FirstAttribute() && !frame) {
    throw mjXError(section, "World body cannot have attributes");
  }

  // iterate over sub-elements; attributes set while parsing parent body
  elem = FirstChildElement(section);
  while (elem) {
    // get sub-element name
    name = elem->Value();

    // get class if specified, otherwise use body
    mjsDefault* def = GetClass(elem);
    if (!def) {
      def = mjs_getDefault(frame ? frame->element : body->element);
    }

    // inertial sub-element
    if (name=="inertial") {
      // no inertia allowed in world body
      if (mjs_getId(body->element)==0) {
        throw mjXError(elem, "World body cannot have inertia");
      }
      body->explicitinertial = true;
      ReadAttr(elem, "pos", 3, body->ipos, text, true);
      ReadQuat(elem, "quat", body->iquat, text);
      ReadAttr(elem, "mass", 1, &body->mass, text, true);
      ReadAttr(elem, "diaginertia", 3, body->inertia, text);
      bool alt = ReadAlternative(elem, body->ialt);
      bool full = ReadAttr(elem, "fullinertia", 6, body->fullinertia, text);
      if (alt && full) {
        throw mjXError(elem, "fullinertia and orientation specifiers cannot be used together");
      }
    }

    // joint sub-element
    else if (name=="joint") {
      // no joints allowed in world body
      if (mjs_getId(body->element)==0) {
        throw mjXError(elem, "World body cannot have joints");
      }

      // create joint and parse
      mjsJoint* joint = mjs_addJoint(body, def);
      OneJoint(elem, joint);
      mjs_setFrame(joint->element, frame);
    }

    // freejoint sub-element
    else if (name=="freejoint") {
      // no joints allowed in world body
      if (mjs_getId(body->element)==0) {
        throw mjXError(elem, "World body cannot have joints");
      }

      // create free joint without defaults
      mjsJoint* joint = mjs_addFreeJoint(body);
      mjs_setFrame(joint->element, frame);

      // save defaults after creation, to make sure writing is ok
      mjs_setDefault(joint->element, def);

      // read attributes
      string name;
      if (ReadAttrTxt(elem, "name", name)) {
        mjs_setString(joint->name, name.c_str());
      }
      ReadAttrInt(elem, "group", &joint->group);
    }

    // geom sub-element
    else if (name=="geom") {
      // create geom and parse
      mjsGeom* geom = mjs_addGeom(body, def);
      OneGeom(elem, geom);
      mjs_setFrame(geom->element, frame);
    }

    // site sub-element
    else if (name=="site") {
      // create site and parse
      mjsSite* site = mjs_addSite(body,  def);
      OneSite(elem, site);
      mjs_setFrame(site->element, frame);
    }

    // camera sub-element
    else if (name=="camera") {
      // create camera and parse
      mjsCamera* camera = mjs_addCamera(body, def);
      OneCamera(elem, camera);
      mjs_setFrame(camera->element, frame);
    }

    // light sub-element
    else if (name=="light") {
      // create light and parse
      mjsLight* light = mjs_addLight(body, def);
      OneLight(elem, light);
      mjs_setFrame(light->element, frame);
    }

    // plugin sub-element
    else if (name == "plugin") {
      OnePlugin(elem, &(body->plugin));
    }

    // composite sub-element
    else if (name=="composite") {
      // parse composite
      OneComposite(elem, body, def);
    }

    // flexcomp sub-element
    else if (name=="flexcomp") {
      // parse flexcomp
      OneFlexcomp(elem, body, vfs);
    }

    // frame sub-element
    else if (name=="frame") {
      // read childdef
      mjsDefault* childdef = 0;
      if (ReadAttrTxt(elem, "childclass", text)) {
        childdef = mjs_findDefault(spec, text.c_str());
        mjs_findDefault(spec, text.c_str());
        if (!childdef) {
          throw mjXError(elem, "unknown default childclass");
        }
      }

      // create frame
      mjsFrame* pframe = mjs_addFrame(body, frame);
      mjs_setString(pframe->info, ("line " + std::to_string(elem->GetLineNum())).c_str());
      mjs_setDefault(pframe->element, childdef ? childdef : def);

      // read attributes
      string name, childclass;
      if (ReadAttrTxt(elem, "name", name)) {
        mjs_setString(pframe->name, name.c_str());
      }
      if (ReadAttrTxt(elem, "childclass", childclass)) {
        mjs_setString(pframe->childclass, childclass.c_str());
      }
      ReadAttr(elem, "pos", 3, pframe->pos, text);
      ReadQuat(elem, "quat", pframe->quat, text);
      ReadAlternative(elem, pframe->alt);

      Body(elem, body, pframe, vfs);
    }

    // replicate sub-element
    else if (name=="replicate") {
      int count;
      double offset[3] = {0, 0, 0};
      double euler[3] = {0, 0, 0};
      string separator = "";
      ReadAttr(elem, "count", 1, &count, text, true);
      ReadAttr(elem, "offset", 3, offset, text);
      ReadAttr(elem, "euler", 3, euler, text);
      ReadAttrTxt(elem, "sep", separator);

      // store rotation difference
      mjsOrientation alt;
      mjs_defaultOrientation(&alt);
      alt.type = mjORIENTATION_EULER;
      mjuu_copyvec(alt.euler, euler, 3);
      double rotation[4] = {1, 0, 0, 0};
      mjs_resolveOrientation(rotation, spec->degree, spec->eulerseq, &alt);

      // read childdef
      mjsDefault* childdef = 0;
      if (ReadAttrTxt(elem, "childclass", text)) {
        childdef = mjs_findDefault(spec, text.c_str());
        mjs_findDefault(spec, text.c_str());
        if (!childdef) {
          throw mjXError(elem, "unknown default childclass");
        }
      }

      // create subtree
      mjsBody* subtree = mjs_addBody(body, childdef);
      double pos[3] = {0, 0, 0};
      double quat[4] = {1, 0, 0, 0};

      // parent frame that will be used to attach the subtree
      mjsFrame* pframe = mjs_addFrame(subtree, frame);
      mjs_setDefault(pframe->element, childdef ? childdef : def);
      mjs_setString(pframe->info, ("line = " + std::to_string(elem->GetLineNum())).c_str());

      // parse subtree
      Body(elem, subtree, pframe, vfs);

      // update pframe and attach
      for (int i = 0; i < count; i++) {
        // accumulate rotation
        mjuu_setvec(pframe->pos, pos[0], pos[1], pos[2]);
        mjuu_frameaccum(pos, quat, offset, rotation);

        // overwrite orientation to increase precision
        alt.euler[0] = i*euler[0];
        alt.euler[1] = i*euler[1];
        alt.euler[2] = i*euler[2];
        mjs_resolveOrientation(quat, spec->degree, spec->eulerseq, &alt);
        mjuu_setvec(pframe->quat, quat[0], quat[1], quat[2], quat[3]);

        // process suffix
        string suffix = separator;
        UpdateString(suffix, count, i);

        // attach to parent
        if (mjs_attachFrame(body, pframe, /*prefix=*/"", suffix.c_str()) != 0) {
          throw mjXError(elem, mjs_getError(spec));
        }
      }

      // delete subtree
      mjs_detachBody(spec, subtree);
    }

    // body sub-element
    else if (name=="body") {
      // read childdef
      mjsDefault* childdef = 0;
      if (ReadAttrTxt(elem, "childclass", text)) {
        childdef = mjs_findDefault(spec, text.c_str());
        mjs_findDefault(spec, text.c_str());
        if (!childdef) {
          throw mjXError(elem, "unknown default childclass");
        }
      }

      // create child body
      mjsBody* child = mjs_addBody(body, childdef);
      mjs_setString(child->info, string("line " + std::to_string(elem->GetLineNum())).c_str());

      // set default from class or childclass
      mjs_setDefault(child->element, childdef ? childdef : def);

      // read attributes
      string name, childclass;
      if (ReadAttrTxt(elem, "name", name)) {
        mjs_setString(child->name, name.c_str());
      }
      if (ReadAttrTxt(elem, "childclass", childclass)) {
        mjs_setString(child->childclass, childclass.c_str());
      }
      ReadAttr(elem, "pos", 3, child->pos, text);
      ReadQuat(elem, "quat", child->quat, text);
      if (MapValue(elem, "mocap", &n, bool_map, 2)) {
        child->mocap = (n==1);
      }
      ReadAlternative(elem, child->alt);

      // read gravcomp
      ReadAttr(elem, "gravcomp", 1, &child->gravcomp, text);

      // read userdata
      std::vector<double> userdata;
      ReadVector(elem, "user", userdata, text);
      mjs_setDouble(child->userdata, userdata.data(), userdata.size());

      // add frame
      mjs_setFrame(child->element, frame);

      // make recursive call
      Body(elem, child, nullptr, vfs);
    }

    // attachment
    else if (name=="attach") {
      string model_name, body_name, prefix;
      ReadAttrTxt(elem, "model", model_name);
      ReadAttrTxt(elem, "body", body_name);
      ReadAttrTxt(elem, "prefix", prefix);

      mjsBody* child = mjs_findBody(spec, (prefix+body_name).c_str());
      mjsFrame* pframe = frame ? frame : mjs_addFrame(body, nullptr);

      if (!child) {
        mjSpec* asset = mjs_findSpec(spec, model_name.c_str());
        if (!asset) {
          throw mjXError(0, "could not find model '%s'", model_name.c_str());
        }
        child = mjs_findBody(asset, body_name.c_str());
        if (!child) {
          throw mjXError(0, "could not find body '%s''%s'", body_name.c_str());
        }
        if (mjs_attachBody(pframe, child, prefix.c_str(), "") != 0) {
          mj_deleteSpec(asset);
          throw mjXError(elem, mjs_getError(spec));
        }
      } else {
        // only set frame to existing body
        mjs_setFrame(child->element, pframe);
      }
    }

    // no match
    else {
      throw mjXError(elem, "unrecognized model element '%s'", name.c_str());
    }

    // advance to next element
    elem = NextSiblingElement(elem);
  }
}



// contact section parser
void mjXReader::Contact(XMLElement* section) {
  string text, name;
  XMLElement* elem;

  // iterate over child elements
  elem = FirstChildElement(section);
  while (elem) {
    // get sub-element name
    name = elem->Value();

    // get class if specified, otherwise use default0
    mjsDefault* def = GetClass(elem);
    if (!def) {
      def = mjs_getSpecDefault(spec);
    }

    // geom pair to include
    if (name=="pair") {
      // create pair and parse
      mjsPair* pair = mjs_addPair(spec, def);
      OnePair(elem, pair);
    }

    // body pair to exclude
    else if (name=="exclude") {
      mjsExclude* exclude = mjs_addExclude(spec);
      string exname, exbody1, exbody2;

      // write error info
      mjs_setString(exclude->info, ("line " + std::to_string(elem->GetLineNum())).c_str());

      // read name and body names
      if (ReadAttrTxt(elem, "name", exname)) {
        mjs_setString(exclude->name, exname.c_str());
      }
      ReadAttrTxt(elem, "body1", exbody1, true);
      mjs_setString(exclude->bodyname1, exbody1.c_str());
      ReadAttrTxt(elem, "body2", exbody2, true);
      mjs_setString(exclude->bodyname2, exbody2.c_str());
    }

    // advance to next element
    elem = NextSiblingElement(elem);
  }
}



// constraint section parser
void mjXReader::Equality(XMLElement* section) {
  XMLElement* elem;

  // iterate over child elements
  elem = FirstChildElement(section);
  while (elem) {
    // get class if specified, otherwise use default0
    mjsDefault* def = GetClass(elem);
    if (!def) {
      def = mjs_getSpecDefault(spec);
    }

    // create equality constraint and parse
    mjsEquality* equality = mjs_addEquality(spec, def);
    OneEquality(elem, equality);

    // advance to next element
    elem = NextSiblingElement(elem);
  }
}



// deformable section parser
void mjXReader::Deformable(XMLElement* section, const mjVFS* vfs) {
  string name;
  XMLElement* elem;

  // iterate over child elements
  elem = FirstChildElement(section);
  while (elem) {
    // get sub-element name
    name = elem->Value();

    // get class if specified, otherwise use default0
    mjsDefault* def = GetClass(elem);
    if (!def) {
      def = mjs_getSpecDefault(spec);
    }

    // flex sub-element
    if (name=="flex") {
      // create flex and parse
      mjsFlex* flex = mjs_addFlex(spec);
      OneFlex(elem, flex);
    }

    // skin sub-element
    else if (name=="skin") {
      // create skin and parse
      mjsSkin* skin = mjs_addSkin(spec);
      OneSkin(elem, skin, vfs);
    }

    // advance to next element
    elem = NextSiblingElement(elem);
  }
}



// tendon section parser
void mjXReader::Tendon(XMLElement* section) {
  string text, text1;
  XMLElement* elem;
  double data;

  // iterate over child elements
  elem = FirstChildElement(section);
  while (elem) {
    // get class if specified, otherwise use default0
    mjsDefault* def = GetClass(elem);
    if (!def) {
      def = mjs_getSpecDefault(spec);
    }

    // create equality constraint and parse
    mjsTendon* tendon = mjs_addTendon(spec, def);
    OneTendon(elem, tendon);

    // process wrap sub-elements
    XMLElement* sub = FirstChildElement(elem);
    while (sub) {
      // get wrap type
      string type = sub->Value();
      mjsWrap* wrap;;

      // read attributes depending on type
      if (type=="site") {
        ReadAttrTxt(sub, "site", text, true);
        wrap = mjs_wrapSite(tendon, text.c_str());
      }

      else if (type=="geom") {
        ReadAttrTxt(sub, "geom", text, true);
        if (!ReadAttrTxt(sub, "sidesite", text1)) {
          text1.clear();
        }
        wrap = mjs_wrapGeom(tendon, text.c_str(), text1.c_str());
      }

      else if (type=="pulley") {
        ReadAttr(sub, "divisor", 1, &data, text, true);
        wrap = mjs_wrapPulley(tendon, data);
      }

      else if (type=="joint") {
        ReadAttrTxt(sub, "joint", text, true);
        ReadAttr(sub, "coef", 1, &data, text1, true);
        wrap = mjs_wrapJoint(tendon, text.c_str(), data);
      }

      else {
        throw mjXError(sub, "unknown wrap type");  // SHOULD NOT OCCUR
      }

      mjs_setString(wrap->info, ("line " + std::to_string(sub->GetLineNum())).c_str());

      // advance to next sub-element
      sub = NextSiblingElement(sub);
    }

    // advance to next element
    elem = NextSiblingElement(elem);
  }
}



// actuator section parser
void mjXReader::Actuator(XMLElement* section) {
  XMLElement* elem;

  // iterate over child elements
  elem = FirstChildElement(section);
  while (elem) {
    // get class if specified, otherwise use default0
    mjsDefault* def = GetClass(elem);
    if (!def) {
      def = mjs_getSpecDefault(spec);
    }

    // create actuator and parse
    mjsActuator* actuator = mjs_addActuator(spec, def);
    OneActuator(elem, actuator);

    // advance to next element
    elem = NextSiblingElement(elem);
  }
}



// sensor section parser
void mjXReader::Sensor(XMLElement* section) {
  int n;
  XMLElement* elem = FirstChildElement(section);
  while (elem) {
    // create sensor, get string type
    mjsSensor* sensor = mjs_addSensor(spec);
    string type = elem->Value();
    string text, name, objname, refname;
    std::vector<double> userdata;

    // read name, noise, userdata
    if (ReadAttrTxt(elem, "name", name)) {
      mjs_setString(sensor->name, name.c_str());
    }
    ReadAttr(elem, "cutoff", 1, &sensor->cutoff, text);
    ReadAttr(elem, "noise", 1, &sensor->noise, text);
    if (ReadVector(elem, "user", userdata, text)) {
      mjs_setDouble(sensor->userdata, userdata.data(), userdata.size());
    }

    // common robotic sensors, attached to a site
    if (type=="touch") {
      sensor->type = mjSENS_TOUCH;
      sensor->objtype = mjOBJ_SITE;
      ReadAttrTxt(elem, "site", objname, true);
    } else if (type=="accelerometer") {
      sensor->type = mjSENS_ACCELEROMETER;
      sensor->objtype = mjOBJ_SITE;
      ReadAttrTxt(elem, "site", objname, true);
    } else if (type=="velocimeter") {
      sensor->type = mjSENS_VELOCIMETER;
      sensor->objtype = mjOBJ_SITE;
      ReadAttrTxt(elem, "site", objname, true);
    } else if (type=="gyro") {
      sensor->type = mjSENS_GYRO;
      sensor->objtype = mjOBJ_SITE;
      ReadAttrTxt(elem, "site", objname, true);
    } else if (type=="force") {
      sensor->type = mjSENS_FORCE;
      sensor->objtype = mjOBJ_SITE;
      ReadAttrTxt(elem, "site", objname, true);
    } else if (type=="torque") {
      sensor->type = mjSENS_TORQUE;
      sensor->objtype = mjOBJ_SITE;
      ReadAttrTxt(elem, "site", objname, true);
    } else if (type=="magnetometer") {
      sensor->type = mjSENS_MAGNETOMETER;
      sensor->objtype = mjOBJ_SITE;
      ReadAttrTxt(elem, "site", objname, true);
    } else if (type=="camprojection") {
      sensor->type = mjSENS_CAMPROJECTION;
      sensor->objtype = mjOBJ_SITE;
      ReadAttrTxt(elem, "site", objname, true);
      ReadAttrTxt(elem, "camera", refname, true);
      sensor->reftype = mjOBJ_CAMERA;
    } else if (type=="rangefinder") {
      sensor->type = mjSENS_RANGEFINDER;
      sensor->objtype = mjOBJ_SITE;
      ReadAttrTxt(elem, "site", objname, true);
    }

    // sensors related to scalar joints, tendons, actuators
    else if (type=="jointpos") {
      sensor->type = mjSENS_JOINTPOS;
      sensor->objtype = mjOBJ_JOINT;
      ReadAttrTxt(elem, "joint", objname, true);
    } else if (type=="jointvel") {
      sensor->type = mjSENS_JOINTVEL;
      sensor->objtype = mjOBJ_JOINT;
      ReadAttrTxt(elem, "joint", objname, true);
    } else if (type=="tendonpos") {
      sensor->type = mjSENS_TENDONPOS;
      sensor->objtype = mjOBJ_TENDON;
      ReadAttrTxt(elem, "tendon", objname, true);
    } else if (type=="tendonvel") {
      sensor->type = mjSENS_TENDONVEL;
      sensor->objtype = mjOBJ_TENDON;
      ReadAttrTxt(elem, "tendon", objname, true);
    } else if (type=="actuatorpos") {
      sensor->type = mjSENS_ACTUATORPOS;
      sensor->objtype = mjOBJ_ACTUATOR;
      ReadAttrTxt(elem, "actuator", objname, true);
    } else if (type=="actuatorvel") {
      sensor->type = mjSENS_ACTUATORVEL;
      sensor->objtype = mjOBJ_ACTUATOR;
      ReadAttrTxt(elem, "actuator", objname, true);
    } else if (type=="actuatorfrc") {
      sensor->type = mjSENS_ACTUATORFRC;
      sensor->objtype = mjOBJ_ACTUATOR;
      ReadAttrTxt(elem, "actuator", objname, true);
    } else if (type=="jointactuatorfrc") {
      sensor->type = mjSENS_JOINTACTFRC;
      sensor->objtype = mjOBJ_JOINT;
      ReadAttrTxt(elem, "joint", objname, true);
    }

    // sensors related to ball joints
    else if (type=="ballquat") {
      sensor->type = mjSENS_BALLQUAT;
      sensor->objtype = mjOBJ_JOINT;
      ReadAttrTxt(elem, "joint", objname, true);
    } else if (type=="ballangvel") {
      sensor->type = mjSENS_BALLANGVEL;
      sensor->objtype = mjOBJ_JOINT;
      ReadAttrTxt(elem, "joint", objname, true);
    }

    // joint and tendon limit sensors
    else if (type=="jointlimitpos") {
      sensor->type = mjSENS_JOINTLIMITPOS;
      sensor->objtype = mjOBJ_JOINT;
      ReadAttrTxt(elem, "joint", objname, true);
    } else if (type=="jointlimitvel") {
      sensor->type = mjSENS_JOINTLIMITVEL;
      sensor->objtype = mjOBJ_JOINT;
      ReadAttrTxt(elem, "joint", objname, true);
    } else if (type=="jointlimitfrc") {
      sensor->type = mjSENS_JOINTLIMITFRC;
      sensor->objtype = mjOBJ_JOINT;
      ReadAttrTxt(elem, "joint", objname, true);
    } else if (type=="tendonlimitpos") {
      sensor->type = mjSENS_TENDONLIMITPOS;
      sensor->objtype = mjOBJ_TENDON;
      ReadAttrTxt(elem, "tendon", objname, true);
    } else if (type=="tendonlimitvel") {
      sensor->type = mjSENS_TENDONLIMITVEL;
      sensor->objtype = mjOBJ_TENDON;
      ReadAttrTxt(elem, "tendon", objname, true);
    } else if (type=="tendonlimitfrc") {
      sensor->type = mjSENS_TENDONLIMITFRC;
      sensor->objtype = mjOBJ_TENDON;
      ReadAttrTxt(elem, "tendon", objname, true);
    }

    // sensors attached to an object with spatial frame: (x)body, geom, site, camera
    else if (type=="framepos") {
      sensor->type = mjSENS_FRAMEPOS;
      ReadAttrTxt(elem, "objtype", text, true);
      sensor->objtype = (mjtObj)mju_str2Type(text.c_str());
      ReadAttrTxt(elem, "objname", objname, true);
      if (ReadAttrTxt(elem, "reftype", text)) {
        sensor->reftype = (mjtObj)mju_str2Type(text.c_str());
        ReadAttrTxt(elem, "refname", refname, true);
      } else if (ReadAttrTxt(elem, "refname", text)) {
        throw mjXError(elem, "refname '%s' given but reftype is missing", text.c_str());
      }
    } else if (type=="framequat") {
      sensor->type = mjSENS_FRAMEQUAT;
      ReadAttrTxt(elem, "objtype", text, true);
      sensor->objtype = (mjtObj)mju_str2Type(text.c_str());
      ReadAttrTxt(elem, "objname", objname, true);
      if (ReadAttrTxt(elem, "reftype", text)) {
        sensor->reftype = (mjtObj)mju_str2Type(text.c_str());
        ReadAttrTxt(elem, "refname", refname, true);
      } else if (ReadAttrTxt(elem, "refname", text)) {
        throw mjXError(elem, "refname '%s' given but reftype is missing", text.c_str());
      }
    } else if (type=="framexaxis") {
      sensor->type = mjSENS_FRAMEXAXIS;
      ReadAttrTxt(elem, "objtype", text, true);
      sensor->objtype = (mjtObj)mju_str2Type(text.c_str());
      ReadAttrTxt(elem, "objname", objname, true);
      if (ReadAttrTxt(elem, "reftype", text)) {
        sensor->reftype = (mjtObj)mju_str2Type(text.c_str());
        ReadAttrTxt(elem, "refname", refname, true);
      } else if (ReadAttrTxt(elem, "refname", text)) {
        throw mjXError(elem, "refname '%s' given but reftype is missing", text.c_str());
      }
    } else if (type=="frameyaxis") {
      sensor->type = mjSENS_FRAMEYAXIS;
      ReadAttrTxt(elem, "objtype", text, true);
      sensor->objtype = (mjtObj)mju_str2Type(text.c_str());
      ReadAttrTxt(elem, "objname", objname, true);
      if (ReadAttrTxt(elem, "reftype", text)) {
        sensor->reftype = (mjtObj)mju_str2Type(text.c_str());
        ReadAttrTxt(elem, "refname", refname, true);
      } else if (ReadAttrTxt(elem, "refname", text)) {
        throw mjXError(elem, "refname '%s' given but reftype is missing", text.c_str());
      }
    } else if (type=="framezaxis") {
      sensor->type = mjSENS_FRAMEZAXIS;
      ReadAttrTxt(elem, "objtype", text, true);
      sensor->objtype = (mjtObj)mju_str2Type(text.c_str());
      ReadAttrTxt(elem, "objname", objname, true);
      if (ReadAttrTxt(elem, "reftype", text)) {
        sensor->reftype = (mjtObj)mju_str2Type(text.c_str());
        ReadAttrTxt(elem, "refname", refname, true);
      } else if (ReadAttrTxt(elem, "refname", text)) {
        throw mjXError(elem, "refname '%s' given but reftype is missing", text.c_str());
      }
    } else if (type=="framelinvel") {
      sensor->type = mjSENS_FRAMELINVEL;
      ReadAttrTxt(elem, "objtype", text, true);
      sensor->objtype = (mjtObj)mju_str2Type(text.c_str());
      ReadAttrTxt(elem, "objname", objname, true);
      if (ReadAttrTxt(elem, "reftype", text)) {
        sensor->reftype = (mjtObj)mju_str2Type(text.c_str());
        ReadAttrTxt(elem, "refname", refname, true);
      } else if (ReadAttrTxt(elem, "refname", text)) {
        throw mjXError(elem, "refname '%s' given but reftype is missing", text.c_str());
      }
    } else if (type=="frameangvel") {
      sensor->type = mjSENS_FRAMEANGVEL;
      ReadAttrTxt(elem, "objtype", text, true);
      sensor->objtype = (mjtObj)mju_str2Type(text.c_str());
      ReadAttrTxt(elem, "objname", objname, true);
      if (ReadAttrTxt(elem, "reftype", text)) {
        sensor->reftype = (mjtObj)mju_str2Type(text.c_str());
        ReadAttrTxt(elem, "refname", refname, true);
      } else if (ReadAttrTxt(elem, "refname", text)) {
        throw mjXError(elem, "refname '%s' given but reftype is missing", text.c_str());
      }
    } else if (type=="framelinacc") {
      sensor->type = mjSENS_FRAMELINACC;
      ReadAttrTxt(elem, "objtype", text, true);
      sensor->objtype = (mjtObj)mju_str2Type(text.c_str());
      ReadAttrTxt(elem, "objname", objname, true);
    } else if (type=="frameangacc") {
      sensor->type = mjSENS_FRAMEANGACC;
      ReadAttrTxt(elem, "objtype", text, true);
      sensor->objtype = (mjtObj)mju_str2Type(text.c_str());
      ReadAttrTxt(elem, "objname", objname, true);
    }

    // sensors related to kinematic subtrees; attached to a body (which is the subtree root)
    else if (type=="subtreecom") {
      sensor->type = mjSENS_SUBTREECOM;
      sensor->objtype = mjOBJ_BODY;
      ReadAttrTxt(elem, "body", objname, true);
    } else if (type=="subtreelinvel") {
      sensor->type = mjSENS_SUBTREELINVEL;
      sensor->objtype = mjOBJ_BODY;
      ReadAttrTxt(elem, "body", objname, true);
    } else if (type=="subtreeangmom") {
      sensor->type = mjSENS_SUBTREEANGMOM;
      sensor->objtype = mjOBJ_BODY;
      ReadAttrTxt(elem, "body", objname, true);
    }

    // sensors for geometric distance; attached to geoms or bodies
    else if (type=="distance" || type=="normal" || type=="fromto") {
      bool has_body1 = ReadAttrTxt(elem, "body1", objname);
      bool has_geom1 = ReadAttrTxt(elem, "geom1", objname);
      if (has_body1 == has_geom1) {
        throw mjXError(elem, "exactly one of (geom1, body1) must be specified");
      }
      sensor->objtype = has_body1 ? mjOBJ_BODY : mjOBJ_GEOM;
      bool has_body2 = ReadAttrTxt(elem, "body2", refname);
      bool has_geom2 = ReadAttrTxt(elem, "geom2", refname);
      if (has_body2 == has_geom2) {
        throw mjXError(elem, "exactly one of (geom2, body2) must be specified");
      }
      sensor->reftype = has_body2 ? mjOBJ_BODY : mjOBJ_GEOM;
      if (type=="distance") {
        sensor->type = mjSENS_GEOMDIST;
      } else if (type=="normal") {
        sensor->type = mjSENS_GEOMNORMAL;
      } else {
        sensor->type = mjSENS_GEOMFROMTO;
      }
    }

    // global sensors
    else if (type=="clock") {
      sensor->type = mjSENS_CLOCK;
      sensor->objtype = mjOBJ_UNKNOWN;
    }

    // user-defined sensor
    else if (type=="user") {
      sensor->type = mjSENS_USER;
      bool objname_given = ReadAttrTxt(elem, "objname", objname);
      if (ReadAttrTxt(elem, "objtype", text)) {
        if (!objname_given) {
          throw mjXError(elem, "objtype '%s' given but objname is missing", text.c_str());
        }
        sensor->objtype = (mjtObj)mju_str2Type(text.c_str());
      } else if (objname_given) {
        throw mjXError(elem, "objname '%s' given but objtype is missing", objname.c_str());
      }
      ReadAttrInt(elem, "dim", &sensor->dim, true);

      // keywords
      if (MapValue(elem, "needstage", &n, stage_map, stage_sz)) {
        sensor->needstage = (mjtStage)n;
      }
      if (MapValue(elem, "datatype", &n, datatype_map, datatype_sz)) {
       sensor->datatype = (mjtDataType)n;
      }
    }

    else if (type=="plugin") {
      sensor->type = mjSENS_PLUGIN;
      OnePlugin(elem, &sensor->plugin);
      ReadAttrTxt(elem, "objtype", text);
      sensor->objtype = (mjtObj)mju_str2Type(text.c_str());
      ReadAttrTxt(elem, "objname", objname);
      if (sensor->objtype != mjOBJ_UNKNOWN && objname.empty()) {
        throw mjXError(elem, "objtype is specified but objname is not");
      }
      if (sensor->objtype == mjOBJ_UNKNOWN && !objname.empty()) {
        throw mjXError(elem, "objname is specified but objtype is not");
      }
      if (ReadAttrTxt(elem, "reftype", text)) {
        sensor->reftype = (mjtObj)mju_str2Type(text.c_str());
      }
      ReadAttrTxt(elem, "refname", refname);
      if (sensor->reftype != mjOBJ_UNKNOWN && refname.empty()) {
        throw mjXError(elem, "reftype is specified but refname is not");
      }
      if (sensor->reftype == mjOBJ_UNKNOWN && !refname.empty()) {
        throw mjXError(elem, "refname is specified but reftype is not");
      }
    }

    if (!objname.empty()) {
      mjs_setString(sensor->objname, objname.c_str());
    }

    if (!refname.empty()) {
      mjs_setString(sensor->refname, refname.c_str());
    }

    // write info
    mjs_setString(sensor->info, ("line " + std::to_string(elem->GetLineNum())).c_str());

    // advance to next element
    elem = NextSiblingElement(elem);
  }
}



// keyframe section parser
void mjXReader::Keyframe(XMLElement* section) {
  XMLElement* elem;
  int n;
  double data[1000];

  // iterate over child elements
  elem = FirstChildElement(section);
  while (elem) {
    string text, name = "";

    // add keyframe
    mjsKey* key = mjs_addKey(spec);

    // read name, time
    ReadAttrTxt(elem, "name", name);
    mjs_setString(key->name, name.c_str());
    ReadAttr(elem, "time", 1, &key->time, text);

    // read qpos
    n = ReadAttr(elem, "qpos", 1000, data, text, false, false);
    if (n) {
      mjs_setDouble(key->qpos, data, n);
    }

    // read qvel
    n = ReadAttr(elem, "qvel", 1000, data, text, false, false);
    if (n) {
      mjs_setDouble(key->qvel, data, n);
    }

    // read act
    n = ReadAttr(elem, "act", 1000, data, text, false, false);
    if (n) {
      mjs_setDouble(key->act, data, n);
    }

    // read mpos
    n = ReadAttr(elem, "mpos", 1000, data, text, false, false);
    if (n) {
      mjs_setDouble(key->mpos, data, n);
    }

    // read mquat
    n = ReadAttr(elem, "mquat", 1000, data, text, false, false);
    if (n) {
      mjs_setDouble(key->mquat, data, n);
    }

    // read ctrl
    n = ReadAttr(elem, "ctrl", 1000, data, text, false, false);
    if (n) {
      mjs_setDouble(key->ctrl, data, n);
    }

    // advance to next element
    elem = NextSiblingElement(elem);
  }
}



// get defaults class
mjsDefault* mjXReader::GetClass(XMLElement* section) {
  string text;
  mjsDefault* def = nullptr;

  if (ReadAttrTxt(section, "class", text)) {
    def = mjs_findDefault(spec, text.c_str());
    if (!def) {
      throw mjXError(
          section,
          string("unknown default class name '" + text + "'").c_str());
    }
  }

  return def;
}

void mjXReader::SetModelFileDir(const string& modelfiledir) {
  modelfiledir_ = FilePath(modelfiledir);
}

void mjXReader::SetAssetDir(const string& assetdir) {
  assetdir_ = FilePath(assetdir);
}

void mjXReader::SetMeshDir(const string& meshdir) {
  meshdir_ = FilePath(meshdir);
}

void mjXReader::SetTextureDir(const string& texturedir) {
  texturedir_ = FilePath(texturedir);
}

FilePath mjXReader::AssetDir() const {
  return modelfiledir_ + assetdir_;
}

FilePath mjXReader::MeshDir() const {
  if (meshdir_.empty()) {
    return AssetDir();
  }
  return modelfiledir_ + meshdir_;
}
FilePath mjXReader::TextureDir() const {
  if (texturedir_.empty()) {
    return AssetDir();
  }
  return modelfiledir_ + texturedir_;
}