Better if context-fill was "opt in" for OT-SVG

Adobe & at least a couple of other companies & foundries, when creating an OT-SVG font by assembling existing SVG artwork, have encountered the same “surprise” now and then in recent months.

The standalone artwork isn’t always explicit about specifying color “black” – resulting in unexpected colors when the corresponding OT-SVG glyph is displayed with the text color set to something other than black in conforming implementations (the stylesheet at https://www.microsoft.com/typography/otspec/svg.htm sets fill to context-fill).

Tools for creating SVG such as Adobe Illustrator will not emit explicit coloration for black when exporting to SVG. This significantly contributes to this particular issue, since Illustrator is a major tool for designing SVG artwork.

It seems that an OT-SVG font designer should explicitly “opt in” when desiring that a portion of the glyph be set to context-fill, since this would be the somewhat unusual case, and thus a conscious design decision.

We are still in the initial stages of OT-SVG adoption, & it would seem to be appropriate to adjust things in the spec now rather than later.

Thoughts?

Sairus