Improve documentation related to mjSpec element deletion.

PiperOrigin-RevId: 775677830
Change-Id: I02e51b57956b0b6a20c654326b54e001b498dd96

doc/changelog.rst

@@ -8,8 +8,7 @@ Upcoming version (not yet released)
 .. admonition:: Breaking API changes
    :class: attention
 
-   - The functions ``mjs_detachBody`` and ``mjs_detachDefault`` have been replaced by :ref:`mjs_delete`. Additionally,
-     `:ref:mjs_detach` was added in order to remove an element from the spec without deleting it.
+   - The functions ``mjs_detachBody`` and ``mjs_detachDefault`` have been replaced by :ref:`mjs_delete`.
    - The Python functions ``element.delete`` have been replaced by ``spec.delete(element)``.
 
 General

doc/programming/modeledit.rst

@@ -96,25 +96,37 @@ Elements cannot be created directly; they are returned to the user by the corres
    my_geom->type = mjGEOM_BOX;                                    // set geom type
    my_geom->size[0] = my_geom->size[1] = my_geom->size[2] = 0.5;  // set box size
    mjModel* model = mj_compile(spec, NULL);                       // compile to mjModel
+   ...
+   mj_deleteModel(model);                                         // free model
+   mj_deleteSpec(spec);                                           // free spec
 
 The ``NULL`` second argument to :ref:`mjs_addGeom` is the optional default class pointer. When using defaults
 procedurally, default classes are passed in explicitly to element constructors. The global defaults of all elements
 (used when no default class is passed in) can be inspected in
 `user_init.c <https://github.com/google-deepmind/mujoco/blob/main/src/user/user_init.c>`__.
 
+.. _meMemory:
+
+Memory management
+^^^^^^^^^^^^^^^^^
+
+As seen in the examples above, model elements are never allocated by the user directly, but rather returned by a
+constructor. The library takes ownership of all elements and frees them when the parent :ref:`mjSpec` is deleted using
+:ref:`mj_deleteSpec`. The user is only responsible for freeing :ref:`mjSpec` structs.
+
 .. _meAttachment:
 
 Attachment
 ^^^^^^^^^^
 
-This framework introduces a powerful new feature: attaching and detaching model subtrees. This feature is already used
-to power the :ref:`attach<body-attach>` an :ref:`replicate<replicate>` meta-elements in MJCF. Attachment allows the user
-to move or copy a subtree from one model into another, while also copying or moving related referenced assets and
-referencing elements from outside the kinematic tree (e.g., actuators and sensors). Similarly, detaching a subtree will
-remove all associated elements from the model. The default behavior is to move the child into the parent while
-attaching, so subsequent changes to the child will also change the parent. Alternatively, the user can choose to make an
-entirely new copy during attach using :ref:`mjs_setDeepCopy`. This flag is temporarily set to true while parsing XMLs.
-It is possible to :ref:`attach a body to a frame<mjs_attach>`:
+This framework introduces a powerful new feature: attaching and deleting model subtrees. This feature is already used to
+power the :ref:`attach<body-attach>` an :ref:`replicate<replicate>` meta-elements in MJCF. Attachment allows the user to
+move or copy a subtree from one model into another, while also copying or moving related referenced assets and
+referencing elements from outside the kinematic tree (e.g., actuators and sensors). Similarly, deleting a subtree will
+remove all associated elements from the model. The default behavior ("shallow copy") is to move the child into the
+parent while attaching, so subsequent changes to the child will also change the parent. Alternatively, the user can
+choose to make an entirely new copy during attach using :ref:`mjs_setDeepCopy`. This flag is temporarily set to true
+while parsing XMLs. It is possible to :ref:`attach a body to a frame<mjs_attach>`:
 
 .. code-block:: C
 

doc/python.rst

@@ -605,7 +605,7 @@ Element removal
 ^^^^^^^^^^^^^^^
 The method ``delete()`` removes the corresponding element from the spec, e.g. ``spec.delete(spec.geom('my_geom'))`` will
 remove the geom named "my_geom" and all of the elements that reference it. For elements that can have children (bodies
-and defaults), ``delete`` removes also all of their children. When detaching body subtrees, all elements which reference
+and defaults), ``delete`` also removes all of their children. When deleting body subtrees, all elements which reference
 elements in the subtree, will also be removed.
 
 Tree traversal