Mention the new Implicit-in-velocity Euler integrator in the XML reference.

#mujoco

PiperOrigin-RevId: 465754132
Change-Id: If1578afe00a69bfa6816d8e18d5fdc9296a69dc4

doc/APIreference.rst

@@ -232,6 +232,7 @@ mjtIntegrator
    {
        mjINT_EULER         = 0,        // semi-implicit Euler
        mjINT_RK4                       // 4th-order Runge Kutta
+       mjINT_IMPLICIT                  // implicit in velocity
    } mjtIntegrator;
 
 | Defined in `mjmodel.h <https://github.com/deepmind/mujoco/blob/main/include/mujoco/mjmodel.h>`_

doc/XMLreference.rst

@@ -1758,9 +1758,10 @@ adjust it properly through the XML.
 :at:`o_solref`, :at:`o_solimp`
    These attributes replace the solref and solimp parameters of all active contact pairs when contact override is
    enabled. See :ref:`CSolver` for details.
-:at:`integrator`: :at-val:`[Euler, RK4], "Euler"`
+:at:`integrator`: :at-val:`[Euler, RK4, implicit], "Euler"`
    This attribute selects the numerical :ref:`integrator <geIntegration>` to be used. Currently the available
-   integrators are the semi-implicit Euler method and the fixed-step 4-th order Runge Kutta method.
+   integrators are the semi-implicit Euler method, the fixed-step 4-th order Runge Kutta method, and
+   the Implicit-in-velocity Euler method.
 :at:`collision`: :at-val:`[all, predefined, dynamic], "all"`
    This attribute specifies which geom pairs should be checked for collision; recall :ref:`Collision` in the Computation
    chapter. "predefined" means that only the explicitly-defined contact :ref:`pairs <pair>` are checked. "dynamic" means

doc/changelog.rst

@@ -19,7 +19,7 @@ General
 - Added ``azimuth`` and ``elevation`` attributes to :ref:`visual/global<global>`, defining the initial orientation of
   the free camera at model load time.
  - Added ``mjv_defaultFreeCamera`` which sets the default free camera, respecting the above attributes.
- - ``simulate`` now supports taking a screenshot via a button in the File section or via ``Ctrl-P``.
+- ``simulate`` now supports taking a screenshot via a button in the File section or via ``Ctrl-P``.
 
 Bug fixes
 ^^^^^^^^^