gh-134370 Added clarification on instances annotations

Doc/glossary.rst

@@ -52,6 +52,8 @@ Glossary
       can be retrieved by calling :func:`annotationlib.get_annotations`
       on modules, classes, and functions, respectively.
 
+      Note that an *instance* of a :term:`class` cannot be annotated.
+
       See :term:`variable annotation`, :term:`function annotation`, :pep:`484`,
       :pep:`526`, and :pep:`649`, which describe this functionality.
       Also see :ref:`annotations-howto`

Doc/howto/annotations.rst

@@ -249,3 +249,8 @@ quirks by using :func:`annotationlib.get_annotations` on Python 3.14+ or
 Python, you can avoid these bugs by accessing the annotations from the
 class's :attr:`~type.__dict__`
 (e.g., ``cls.__dict__.get('__annotations__', None)``).
+
+In some versions of Python, instances of classes may have an ``__annotations__``
+attribute. This is not supported functionality, so the best practice is to always
+interact with the ``__annotations__`` attribute of an instance's type. For example
+``type(myinstance).__annotations__``.