Link isinstance/issubclass to the ABC glossary entry (#12256)
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index edff106..3b6fdc3 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -624,7 +624,8 @@
.. function:: isinstance(object, classinfo)
Return true if the *object* argument is an instance of the *classinfo*
- argument, or of a (direct or indirect) subclass thereof. If *object* is not
+ argument, or of a (direct, indirect or :term:`virtual <abstract base
+ class>`) subclass thereof. If *object* is not
an object of the given type, the function always returns false. If
*classinfo* is not a class (type object), it may be a tuple of type objects,
or may recursively contain other such tuples (other sequence types are not
@@ -634,7 +635,8 @@
.. function:: issubclass(class, classinfo)
- Return true if *class* is a subclass (direct or indirect) of *classinfo*. A
+ Return true if *class* is a subclass (direct, indirect or :term:`virtual
+ <abstract base class>`) of *classinfo*. A
class is considered a subclass of itself. *classinfo* may be a tuple of class
objects, in which case every entry in *classinfo* will be checked. In any other
case, a :exc:`TypeError` exception is raised.