====== Proposal CSS Masking ======

---- dataentry ----
Spec_tags     : css-masking        # in alpha order; or "none"
Owner_tags    : dschulze          # Who's driving the discussion?
Status_tags   : Resolved            # [ Open | Resolved | Closed | Pending ] [, Urgent]?
Added_dt      : 2012-08-28        # Date added as WG discussion request

Action        : Resolve to continue on ED # Or, if Pending, pending what?
                # Some Examples:
# Action        : Pick A, B, or C?
# Action        : Approve the proposal?
# Action        : Discuss problem and provide direction?
# Action        : Help research needed info!
# Action        : Help write proposals!
# Action        : Give feedback!
# Action        : Publish FPWD/WD/LC/CR/PR/REC!

Issue_urls    : http://dvcs.w3.org/hg/FXTF/raw-file/tip/masking/index.html
Proposal_urls : 
Agenda_urls   : # If this is part of an ordered series of related topics, e.g. LC issues, use this to link to the supertopic agenda
----

=== Background ===

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:
   * 'mask' as a shorthand for 'mask-image' and other properties deriving from 'background' and 'mask-box-image' as shorthand for properties deriving from 'border-image' (WebKit)
   * 'mask' that takes a <funcIRI> to a 'mask' element to mask arbitrary HTML and SVG content (Firefox)
   * 'clip-path' that takes a <funcIRI> to a 'clipPath' element to clip arbitrary HTML and SVG content (Firefox)

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.

=== Problem Statement ===

  * 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.

=== Resolved ===
  * Go on with ED
  * Keep 'mask-origin'
  * Drop 'mask-attachment'
  * 'mask-clip' must allow extending the region beyond border-box.
  * Keep 'clip-path'
  * Consider making 'clip' shadowing 'clip-path' (or the other way around), 'rect()' would just apply to absolute positioned elements for legacy reasons