documentation update

Author: dg-pb

Doc/library/functools.rst

@@ -378,20 +378,31 @@ The :mod:`functools` module defines the following functions:
       >>> basetwo('10010')
       18
 
-   If ``Placeholder`` sentinels are present in *args*, they will be filled first
+   If :data:`Placeholder` sentinels are present in *args*, they will be filled first
    when :func:`partial` is called. This allows custom selection of positional arguments
    to be pre-filled when constructing :ref:`partial object<partial-objects>`.
-   If ``Placeholder`` sentinels are used, all of them must be filled at call time:
+   If :data:`Placeholder` sentinels are used, all of them must be filled at call time:
 
       >>> from functools import partial, Placeholder
-      >>> say_to_world = partial(print, Placeholder, 'world!')
+      >>> say_to_world = partial(print, Placeholder, Placeholder, "world!")
       >>> say_to_world.placeholder_count
-      1
-      >>> say_to_world('Hello')
-      Hello world!
+      2
+      >>> say_to_world('Hello', 'dear')
+      Hello dear world!
+
+   Calling ``say_to_world('Hello')`` would result in :exc:`TypeError`.
 
    .. versionchanged:: 3.14
-      Support for ``Placeholder`` in *args*
+      Support for :data:`Placeholder` in *args*
+
+.. data:: Placeholder
+
+   This is a singleton object that is used as a sentinel for representing a
+   gap in positional arguments when calling :func:`partial`.
+   It has similar features as :data:`None`:
+
+      >>> type(Placeholder)() is Placeholder
+      True
 
 .. class:: partialmethod(func, /, *args, **keywords)