[cssom] unrecognized rules and properties

The current CSSOM draft has removed support for accessing 
unrecognized rules and properties. This is a regression
IMO.

Below excerpts are from the specs:
old: http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113/css.html
new: http://dev.w3.org/csswg/cssom/

Unrecognized rules:

  old:
    2.2
    Interface CSSRule
    const unsigned short UNKNOWN_RULE = 0;
    ... The CSSUnknownRule interface represents an at-rule 
    not supported by this user agent.

  new:
    7.1.1 
    ... Statements that were dropped during parsing can 
    not be found using these APIs.
    7.2.2
    (UNKNOWN_RULE removed)

Unrecognized properties:

  old:
    2.2
    Interface CSSStyleDeclaration
    ... While an implementation may not recognize all CSS 
    properties within a CSS declaration block, it is 
    expected to provide access to all specified 
    properties in the style sheet through the 
    CSSStyleDeclaration interface.

  new:
    7.3.2
    (no mention)

What case has been made for removing this support? IMO
there are strong arguments for having it.

Best regards
Mike Wilson