Mention metadata bits in overview

Signed-off-by: Michał Górny <mgorny@quansight.com>

Author: mgorny

peps/pep-0817.rst

@@ -737,7 +737,7 @@ described in `modified wheel filename`_, and are characterizing using
 hierarchical structure of namespaces, features and feature values. When
 evaluating wheels to install, the installer determines whether variant
 properties of a given wheel are compatible with the system, and perform
-variant ordering based on the priority of the compatible variant
+`variant ordering`_ based on the priority of the compatible variant
 properties. This is done in addition to determining the compatibility.
 The ordering by variant properties takes precedence over ordering by
 tags.
@@ -751,18 +751,22 @@ embedded in the wheel; it can be either provided directly by the
 wheel maintainer or queried at wheel build time from an AoT plugin.
 
 Both kinds of plugins are usually implemented as Python packages which
-implement the provider plugin API, but they may also be vendored or
+implement the `provider plugin API`_, but they may also be vendored or
 reimplemented by installers to improve security, as outlined in
-`Providers`_.
-
-Plugin packages may be installed in isolated or non-isolated
-environments. In particular, all plugins may be returned by the
-``get_requires_for_build_wheel()`` hook of a :pep:`517` backend, and
+`Providers`_. Plugin packages may be installed in isolated or
+non-isolated environments. In particular, all plugins may be returned by
+the ``get_requires_for_build_wheel()`` hook of a :pep:`517` backend, and
 therefore installed along with other build dependencies. For this
 reason, it is important that plugin packages do not narrowly pin
 dependencies, as that could prevent different packages from being
 installed simultaneously in the same environment.
 
+Metadata governing variant support is defined in ``pyproject.toml``
+file, and it is copied into ``variant.json`` file in wheels, as explored
+in `metadata in source tree and wheels`_. Additionally, `variant
+environment markers`_ can be used to define dependencies specific to a
+subset of variants.
+
 
 Modified wheel filename
 -----------------------