Proposal CSS Masking
The CSS WG and the SVG WG decided to work on a CSS Masking specification in the FXTF. The CSS WG did not decide if the specification should specify the current behavior of browsers:
Further more the new specification unifies both implementations and extends 'clip-path' to take <shape>s from CSS Exclusions as shorthand for clipping beside <funcIRI>.
The CSS WG needs to decide if we continue with the current specification.
Are all properties needed? In question: 'mask-origin', 'mask-attachment' and 'mask-clip'.
Masking/Clipping on Firefox operates on 'bounding client rect', 'mask-image' on WebKit operate on 'border-box', 'content-box' and 'padding-box'. Both behaviors are reasonable.
select() and child are new functions/keywords requested by the SVG
WG. The sense in the HTML
world depends on the definition.
Go on with ED
'mask-clip' must allow extending the region beyond border-box.
Consider making 'clip' shadowing 'clip-path' (or the other way around), 'rect()' would just apply to absolute positioned elements for legacy reasons