Fix mjSpec colab after changing the default behavior of attach to be …

…a shallow copy.

PiperOrigin-RevId: 724375710
Change-Id: I5fac7d24c1d0b1ad4d427c021022c47620accf53

doc/python.rst

@@ -547,16 +547,18 @@ It is possible to combine multiple specs by using attachments. The following opt
     the reference to the attached body, which should be identical to the body used as input.
 -   Attach a frame from the child spec to a body in the parent spec: ``body.attach_frame(frame, prefix, suffix)``,
     returns the reference to the attached frame, which should be identical to the frame used as input.
--   Attach a child spec to a site in the parent spec: ``spec.attach(child_spec, site=site_name_or_obj)``, returns the
-    reference to a frame, which is the attached worldbody transformed into a frame. The site must belong to the child
-    spec. Prefix and suffix can also be specified as keyword arguments.
+-   Attach a child spec to a site in the parent spec: ``parent_spec.attach(child_spec, site=site_name_or_obj)``, returns
+    the reference to a frame, which is the attached worldbody transformed into a frame. The site must belong to the
+    child spec. Prefix and suffix can also be specified as keyword arguments.
 -   Attach a child spec to a frame in the parent spec: ``parent_spec.attach(child_spec, frame=frame_name_or_obj)``,
     returns the reference to a frame, which is the attached worldbody transformed into a frame. The frame must belong to
     the child spec. Prefix and suffix can also be specified as keyword arguments.
 
-Attaching does not copy, so all the child references are still valid in the parent and therefore modifying the child will
-modify the parent. This is not true for the attach :ref:`attach<body-attach>` and :ref:`replicate<replicate>`
-meta-elements in MJCF, which create deep copies while attaching.
+The default behavior of attaching is to not copy, so all the child references (except for the worldbody) are still valid
+in the parent and therefore modifying the child will modify the parent. This is not true for the attach
+:ref:`attach<body-attach>` and :ref:`replicate<replicate>` meta-elements in MJCF, which create deep copies while
+attaching. However, it is possible to override the default behavior by setting ``spec.copy_during_attaching`` to
+``True``. In this case, the child spec is copied and the references to the child will not point to the parent.
 
 .. code-block:: python
 

python/mjspec.ipynb

@@ -368,6 +368,7 @@
     "  \"\"\"Constructs a creature with `num_legs` legs.\"\"\"\n",
     "  rgba = random_state.uniform([0, 0, 0, 1], [1, 1, 1, 1])\n",
     "  spec = mj.MjSpec.from_string(creature_model)\n",
+    "  spec.copy_during_attach = True\n",
     "\n",
     "  # Attach legs to equidistant sites on the circumference.\n",
     "  spec.worldbody.first_geom().rgba = rgba\n",
@@ -672,6 +673,7 @@
     "#@title Humanoid with arms replaced by legs.{vertical-output: true}\n",
     "\n",
     "spec = mj.MjSpec.from_file(humanoid_file)\n",
+    "spec.copy_during_attach = True\n",
     "\n",
     "# Get the torso, arm, and leg bodies\n",
     "arm_left = spec.find_body('upper_arm_left')\n",
@@ -781,6 +783,7 @@
     "\n",
     "humanoid = mj.MjSpec.from_file(humanoid_file)\n",
     "spec = mj.MjSpec()\n",
+    "spec.copy_during_attach = True\n",
     "\n",
     "# Delete all key frames to avoid name conflicts\n",
     "while humanoid.keys:\n",