Fix #13900: resolve self-referential description of a parameter.

Doc/library/email.parser.rst

@@ -135,7 +135,9 @@ class.
       data or by a blank line.  Following the header block is the body of the
       message (which may contain MIME-encoded subparts).
 
-      Optional *headersonly* is as with the :meth:`parse` method.
+      Optional *headersonly* is a flag specifying whether to stop parsing after
+      reading the headers or not.  The default is ``False``, meaning it parses
+      the entire contents of the file.
 
       .. versionchanged:: 2.2.2
          The *headersonly* flag was added.
@@ -148,9 +150,7 @@ class.
       equivalent to wrapping *text* in a :class:`StringIO` instance first and
       calling :meth:`parse`.
 
-      Optional *headersonly* is a flag specifying whether to stop parsing after
-      reading the headers or not.  The default is ``False``, meaning it parses
-      the entire contents of the file.
+      Optional *headersonly* is as with the :meth:`parse` method.
 
       .. versionchanged:: 2.2.2
          The *headersonly* flag was added.