Adjust stroke/fill to be compatible with proposed Fill & Stroke spec

[fantasai]

We had resolved to have stroke/fill be shorthand properties that reset all of the stroke-* or fill-* properties. The SVG2 spec should reflect this, as it is a breaking change (and not a “new feature” that can be deferred).

For stroke there were two possibilities discussed: shorthanding just the paint properties (i.e. not dashing or widths), or shorthanding all stroke-* properties. The latter might be preferable, but compat is a question here.

(This should probably be Agenda+ for TPAC.)

[AmeliaBR]

Who/when was this resolved? If stroke and fill became a reset for any of the SVG 1.1 properties, that would be a huge breaking change, messing up all sorts of content; I would never accept that.

The plan was to make stroke and fill shorthands for the new CSS-background-inspired sizing longhands. But since those were deferred to the proposed new fill & stroke spec, the only change for SVG 2 was to allow lists of multiple paint layers.

[AmeliaBR]

Based on discussion at the 4 August 2016 telcon, we concluded:

• stroke and fill cannot become shorthands for any of the existing properties, as this would be unacceptable for web compatibility
• However, stroke and fill can be expanded as shorthands for new properties to control CSS image types as paint sources, as proposed in the new CSS Fill and Stroke draft spec. E.g., stroke-image and stroke-color will both be reset by stroke.
• There may also be additional new shorthands introduced, such as stroke-dash as a shorthand to set dasharray and dashoffset and the proposed other dashing options.
• In order to give @tabatkins & @fantasai flexibility while developing that spec, and in order to ensure that SVG implementations for layered paint can be updated at the same time as for CSS images, SVG 2 will not have layered paint.
• SVG 2 will still have context-fill and context-stroke keywords; these reset the entire fill/stroke shorthand and will be added to the new CSS spec.
• SVG 2 will still have child references to paint sources, as an alternative to url() references; these will be added to the new spec as an option for individual image values.

[AmeliaBR]

Assigning this to @nikosandronikos because he took an action to make the edits to remove multi-layer paint from SVG 2.