Tweak some wording

Author: taleinat

peps/pep-0661.rst

@@ -155,13 +155,14 @@ also work as expected, returning ``True`` only when the object is compared
 with itself.  Identity checks such as ``if value is MISSING:`` should usually
 be used rather than boolean checks such as ``if value:`` or ``if not value:``.
 
-Sentinel instances are truthy by default, unlike ``None``.  This parallels the
-default for arbitrary classes, as well as the boolean value of ``Ellipsis``.
+Sentinel instances are "truthy", i.e. boolean evaluation will result in
+``True``.  This parallels the default for arbitrary classes, as well as the
+boolean value of ``Ellipsis``. This is unlike ``None``, which is "falsy".
 
 The names of sentinels are unique within each module.  When calling
 ``Sentinel()`` in a module where a sentinel with that name was already
 defined, the existing sentinel with that name will be returned.  Sentinels
-with the same name in different modules will be distinct from each other.
+with the same name from different modules will be distinct from each other.
 
 Creating a copy of a sentinel object, such as by using ``copy.copy()`` or by
 pickling and unpickling, will return the same object.
@@ -174,10 +175,8 @@ not work as intended, such as perhaps when using Jython or IronPython.  This
 parallels the designs of ``Enum`` and ``namedtuple``.  For more details, see
 :pep:`435`.
 
-The ``Sentinel`` class may not be sub-classed, to avoid overly-clever uses
-based on it, such as attempts to use it as a base for implementing singletons.
-It is considered important that the addition of Sentinel to the stdlib should
-add minimal complexity.
+The ``Sentinel`` class may not be sub-classed, to avoid the greater complexity
+of supporting subclassing.
 
 Ordering comparisons are undefined for sentinel objects.