Update 2.7 docs about legal characters allowed in Cookie name

Doc/library/cookie.rst

@@ -22,8 +22,14 @@ cookie value.
 
 The module formerly strictly applied the parsing rules described in the
 :rfc:`2109` and :rfc:`2068` specifications.  It has since been discovered that
-MSIE 3.0x doesn't follow the character rules outlined in those specs.  As a
-result, the parsing rules used are a bit less strict.
+MSIE 3.0x doesn't follow the character rules outlined in those specs and also
+many current day browsers and servers have relaxed parsing rules when comes to
+Cookie handling.  As a result, the parsing rules used are a bit less strict.
+
+The character set, :data:`string.ascii_letters`, :data:`string.digits` and
+``!#$%&'*+-.^_`|~`` denote the set of valid characters allowed by this module
+in Cookie name (as :attr:`~Morsel.key`).
+
 
 .. note::