Define Color Valued Attributes from CSS / HTML5

[fred-wang]

See https://mathml-refresh.github.io/mathml/chapter2.html#fund.units

Let's just drop that definition and just refer to https://drafts.csswg.org/css-color/#typedef-color instead. This is what browsers are going to use.

[fred-wang]

Or maybe it should be the HTML5 one: https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#colours ?

[NSoiffer]

I agree we should just use a pointer to the spec. Since this is in HTML and not CSS, I think the HTML spec is the appropriate one to reference.

[davidcarlisle]

I added a placeholder section to the core spec https://mathml-refresh.github.io/mathml-core/#color

[fred-wang]

cc @bkardell

What is Firefox seems to recognize HTML colors (similar to what is described in the MathML spec) while WebKit/Chromium accepts CSS colors. Compare this:

<p><math mathcolor="red"><mtext>red</mtext></math></p>
<p><math mathcolor="rgb(255,0,0)"><mtext>rgb(255,0,0)</mtext></math></p>

Whatever we decide, we will need WPT tests for these.

[rwlbuis]

I think CSS colors is the way to go since they offer alternative color specification like rgb, rgba and hsl.
SVG1.1 refers to CSS2:
https://www.w3.org/TR/SVG11/types.html#DataTypeColor
SVG2 refers to CSS3:
https://www.w3.org/TR/SVG2/painting.html#ColorProperty

It seems 'transparent' is supported for both mathcolor and mathbackground in Firefox and WebKit, so maybe it should be specified for both attributes.

[fred-wang]

Resolution:

• https://lists.w3.org/Archives/Public/public-mathml4/2019May/0006.html
• "we agree to go with color attributes"

@bkardell, @NSoiffer @rwlbuis Not sure what it is meant by "we agree to go with color attributes". I think we decided to use the CSS syntax.

[bkardell]

Sorry, that is poor minuting on my part. I believe that what I meant to type was something like "we agree to basically follow svg and point to css colors?"

Though, that should mean that both of the above in the example should work, right? red is a valid color name in css as a 'keyword' I think.

[fred-wang]

Right that was my understanding too so yes the two syntaxes in #62 (comment) will work.

[fred-wang]

The spec now refers to CSS colors.

[NSoiffer]

I believe that this is basically resolved so that the only appropriate labels are "needs tests" and "MathML 4" (that spec needs updating).