The complete MJCF surface in one hand-maintained file: 144 elements, 8
shared attribute groups, 47 enums, 1,497 typed attributes with
defaults, the presence-constraint inventory previously visible only as
hand-written reader checks, and the save policies previously visible
only as hand-written writer logic.
The language is a small IDL: elements bound to their mjSpec structs,
typed attributes with arities and defaults, enum keyword sets with C
bindings, reusable and variant groups, explicit name/reference
namespaces (id<ns>/ref<ns>, following dm_control's
identifier/reference model), child cardinalities, presence constraints
(exclusive/together/requires/oneof over attribute bundles), bitwise
flag sets, identity constants (set field = CONST), fixed char arrays
(chars[n], arity counting characters), numeric range facets, and two
escape hatches: reading=custom (no typed binding is generated; both
reading and saving are hand-written) and writing=custom (the binding
drives the reader, the save policy is hand-written).
doc/generate/mjcf_schema.py is the dependency-free parser and semantic
validator; errors report file:line; 55 unit tests. The language is
documented by the cheat-sheet legend at the top of the schema file.
The schema was bootstrapped by extraction from the sources of record --
the MJCF[] table, the mjMap keyword tables, the ~660 ReadAttr*/MapValue
call sites, mjspec.h struct fields, and the default-constructors in
user_init.c and engine_init.c -- then hand-curated. Same-tag elements
that differ by context are distinct declarations carrying an xml=
facet; worldbody, frame and replicate carry alias=body, mirroring
mjXSchema::NameMatch. The top-level order is by dependency, what a
saved file should read like: front matter, declarations before use,
the tree, the sections that reference it, the data tail.
PiperOrigin-RevId: 958060695
Change-Id: Ie10fd9f0ef202a3626f4d635d02c8731a4d287df
Yuval Tassa
3f8db4c17a