fix(markers): Fix/change dependency specifiers

source/specifications/dependency-specifiers.rst

@@ -196,20 +196,31 @@ safely evaluate it without running arbitrary code that could become a security
 vulnerability. Markers were first standardised in :pep:`345`. This document
 fixes some issues that were observed in the design described in :pep:`426`.
 
-Comparisons in marker expressions are typed by the comparison operator and the
-type of the marker value. The <marker_op> operators that are not in
-<version_cmp> perform the same as they do for strings or sets in Python based on
-whether the marker value is a string or set itself. The <version_cmp> operators
-use the version comparison rules of the
-:ref:`Version specifier specification <version-specifiers>` when those are
-defined (that is when both sides have a valid version specifier). If there is no
-defined behaviour of this specification and the operator exists in Python, then
-the operator falls back to the Python behaviour for the types involved.
-Otherwise an error should be raised. e.g. the following will result in errors::
+Comparisons in marker expressions are based on the types in the table below.
+The variables marked with ``Version`` or ``Version | String`` use the version
+comparison rules of the :ref:`Version specifier specification
+<version-specifiers>` when those are defined (that is when both sides have a
+valid version specifier). If either side is not expressible as a ``Version``,
+then ``>=`` and``<=``, are equivalent to ``==``; no ordering is
+assumed.  The ``<`` and ``>`` operators always return false on strings. The
+``===`` legacy arbitrary equivalence operator does an exact, case insensitive
+comparison regardless of if a string fallback is used.  On other operators,
+operators perform the same as they do for strings or sets in Python based on
+whether the marker value is a string or set itself.  Otherwise an error should
+be raised; it should be noted that ``~=`` does not support string fallback.
+e.g. the following will result in errors::
 
     "dog" ~= "fred"
     python_version ~= "surprise"
 
+Variables that are marked solely as ``String`` support ``==`` and ``!=``;
+ordered comparison operators may also follow same rules as ``Version`` defined
+above when one side is not a valid Version, with ``>=`` and ``<=`` being
+equivalent to ``==``, and ``<`` and ``>`` always evaluating to ``False``. This
+is legacy behavior due to an older version of this spec, and tools may choose
+to warn or fail if ordered comparisons are used on ``String`` markers. ``~=``
+and ``====`` (legacy arbitrary equivalence) are not supported on string fields.
+
 User supplied constants are always encoded as strings with either ``'`` or
 ``"`` quote marks. Note that backslash escapes are not defined, but existing
 implementations do support them. They are not included in this
@@ -267,7 +278,7 @@ an error like all other unknown variables.
      - ``CPython``, ``Jython``
    * - ``platform_release``
      - :py:func:`platform.release()`
-     - String
+     - Version | String
      - ``3.14.1-x86_64-linode39``, ``14.5.0``, ``1.8.0_51``
    * - ``platform_system``
      - :py:func:`platform.system()`