Address review feedback

Author: godlygeek

source/specifications/core-metadata.rst

@@ -544,28 +544,27 @@ distribution.
 
 A requirement string has one mandatory and three optional parts.
 
-* A project name, in the same format as the ``Name:`` field.
-  The only mandatory part.
+* A project name, in :ref:`the same format <name-format>`
+  as the ``Name:`` field. The only mandatory part.
 * A comma-separated list of 'extra' names in square brackets, like
   ``[extra1,extra2]``. These names are defined by the required
   project, referring to specific features which may need extra
   dependencies. The names MUST conform to the restrictions specified
   by the ``Provides-Extra:`` field.
-* Either a version specifier or an ``@`` sign followed by a URL.
-  Tools parsing the format should accept optional parentheses around
-  a version specifier, but tools generating it should not use
-  parentheses.
+* Either a :doc:`version specifier <version-specifiers>` or a
+  :doc:`direct reference <direct-references>`. Tools parsing the format
+  should accept optional parentheses around a version specifier, but
+  tools generating it should not use parentheses. If a distribution
+  requires a direct reference it cannot be uploaded to PyPI, but private
+  repositories may allow such distributions.
 * An environment marker after a semicolon. This means that the
   requirement is only needed in the specified conditions.
 
-See :pep:`508` for full details of the allowed format.
+See :ref:`dependency-specifiers` for full details of the allowed format.
 
 The project names should correspond to names as found
 on the `Python Package Index`_.
 
-Version specifiers must follow the rules described in
-:doc:`version-specifiers`.
-
 Examples::
 
     Requires-Dist: pkginfo

source/specifications/version-specifiers.rst

@@ -1078,6 +1078,7 @@ Examples
 * ``~=3.1.0, != 3.1.3``: version 3.1.0 or later, but not version 3.1.3 and
   not version 3.2.0 or later.
 
+.. _direct-references:
 
 Direct references
 =================