Add a class option to the toctree directive (#12524)

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

doc/usage/restructuredtext/basics.rst

@@ -380,6 +380,12 @@ Docutils supports the following directives:
        When the default domain contains a ``class`` directive, this directive
        will be shadowed.  Therefore, Sphinx re-exports it as ``rst-class``.
 
+    .. tip::
+
+       If you want to add a class to a directive,
+       you may consider the ``:class:`` :dudir:`option <common-options>` instead,
+       which is supported by most directives and allows for a more compact notation.
+
 * HTML specifics:
 
   - :dudir:`meta`

doc/usage/restructuredtext/directives.rst

@@ -124,6 +124,14 @@ tables of contents.  The ``toctree`` directive is the central element.
 
          foo
 
+   As with :dudir:`most directives <common-options>`,
+   you can use the ``class`` option to assign `class attributes`_::
+
+      .. toctree::
+         :class: custom-toc
+
+   .. _class attributes: https://docutils.sourceforge.io/docs/ref/doctree.html#classes
+
    If you want only the titles of documents in the tree to show up, not other
    headings of the same level, you can use the ``titlesonly`` option::