Apply author declarations in encapsulation-context order before layer,
specificity, scope proximity, and source-order tie breaking. Normal
author rules now cascade from inner shadow contexts outward. This lets
outer contexts override component defaults. Important author rules
cascade the other way so inner contexts can enforce requirements.
Keep the ordering context-bucketed. The common document-only path still
collects and sorts one author context. Custom properties follow the same
context order. var() substitution now observes the same winners as
longhand properties.
Make revert-layer remove declarations only from the matching cascade
origin, context, and layer. This keeps presentational hints and values
from other shadow contexts available when one context rolls back its own
layer.
Add coverage for document and shadow-host competition, slotted rules,
nested slot contexts, inline styles, important declarations, custom
properties, and revert-layer across shadow contexts.
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