Align definition of space characters with HTML5

[fred-wang]

"In MathML, white spaces are understood as XML spaces (U+0020), tabs
(U+0009), line feeds (U+000A), and carriage returns (U+000D) while HTML5
also includes "form feed" (U+000C).

https://www.w3.org/TR/html5/infrastructure.html#space-character"

originally reported at https://lists.w3.org/Archives/Public/www-math/2016Aug/0000.html

cc @rwlbuis

[fred-wang]

This is for MathML 4 but I think we eventually want to move the space definition to MathML Core.

[davidcarlisle]

If using an html parser we should match html for whitespace, also I think we could probably always include U+000C in any mathml-specified white space handling for whitespace collapse etc, however any change in wording here needs to accommodate xml parsing, we can't can't change xml parse rules so for example

<mfrac> U+000C <mn>1</mn> U+000C <mn>1</mn> </mfrac>

is going to parse as text content in an mfrac if using an xml parser, and so be invalid.

[NSoiffer]

What what it's worth... according to this whatwg doc, "Form feed characters are discouraged in XML 1.1". So saying don't use U+000C shouldn't be a big deal.

[NSoiffer]

Resolved in 29/4/19 meeting to align with HTML5.

[fred-wang]

cc @bkardell

I reopened this since we to update the specs and to write WPT tests. I expect browsers already treat spaces as HTML5.

[fred-wang]

Resolution:

• https://lists.w3.org/Archives/Public/public-mathml4/2019May/0006.html
• agreed to align on HTML5 or CSS

[fred-wang]

CSS definition is "A newline, U+0009 CHARACTER TABULATION, or U+0020 SPACE. "
https://www.w3.org/TR/css-syntax/#whitespace

And newline is
U+000A LINE FEED. Note that U+000D CARRIAGE RETURN and U+000C FORM FEED are not included in this definition, as they are converted to U+000A LINE FEED during preprocessing.

So it seems CSS agrees with HTML, if we take preprocessing into account.

[fred-wang]

I believe in MathML Core this is only used for attribute trimming ( w3c/mathml-core#165 ), menclose@notation ( #104, #105 ) and maybe text nodes ( #28 ). So I think this is already covered by other issues and can be closed.