[cssom-2] Start CSSOM 2

[SebastianZ]

The CSS Object Model spec. is in Working Draft status since 2011 and many new features were added and changes were made over the years.

To let this specification finally progress to CR, I suggest to make a cut regarding new features. Anything extending the interfaces defined there should be added to a new Level 2 spec.
Also, some features currently defined there that require more discussion and/or a proper definition should be deferred to level 2. Which of them to defer needs to be discussed.

Given, this spec. is based on the Document Object Model (DOM) Level 2 Style Specification, which is already a Recommendation, I even put up for discussion whether the spec. should be turned into a Level 3 spec. instead (and a Level 4 spec. created for everything new).

Sebastian

[SebastianZ]

@therealglazou @emilio