This PEP extends PEP 825 by defining how variant properties are governed and how their compatibility is determined. This is done either via static feature and feature value compatibility lists specified in the variant metadata, or by querying opt-in plugins that are Python packages but can also be vendored or reimplemented by the tools. A static list can also be provided in place of querying the plugins. Additionally, an ABI Dependency Variant Provider is defined to facilitate builds of the same package against different dependency versions.