math-variant
explainerThis document proposes new values for the text-transform properties in order to map alphanumeric text to equivalent Mathematical Alphanumeric Symbols. It will help implementers of MathML (or more generally of tools to generate or display math content) by taking care of inheritance, character mapping and miscellaneous other use cases. See math-variant tables for detailed per-character conversion. For further discussions on this proposal see math-variant comments.
<span style="text-transform: math-fraktur">A</span>
would render the same as
<span>đť”„</span>
or <span>𝔄</span>
(U+1D504 MATHEMATICAL FRAKTUR CAPITAL A).
The LaTeX formula
\exp{\mathbf{A}} \in _n\left(\mathbb R\right)}
is written with the exponential function using â€śnormalâ€ť variant,
the matrix A using â€śboldâ€ť variant, the Lie algebra using â€śfrakturâ€ť variant,
the integer n using â€śitalicâ€ť variant and the set of numbers R using â€śdouble-struckâ€ť
variant. The \math*
commands could just be mapped to
equivalent HTML nodes, styled with the text-transform
property.
A simple math formula like
<span style="text-transform: math-italic" style>x + y</span>
would have x, y in
italic but not operator + (contrary to font-style: italic
).
<span style="font-family: STIX Math; text-transform: math-bold">F</span>
would use
the glyph for U+1D46D MATHEMATICAL BOLD ITALIC CAPITAL F contained in the
STIX Math font. It would not try to look into the (non-existent) STIX Math
bold font or emulate bold style from the F glyph of the STIX Math font.
However, if STIX Math font is not available and none of the fonts used
actually have a glyph for U+1D46D it may use this kind of fallback behavior,
as it is done for font-weight: bold
.
Polyfills can emulate MathML behavior of
<mstyle mathvariant="double-struck">...</mstyle>
via mstyle[mathvariant="double-struck"] { text-transform: math-double-struck; }
.
More generally, native implementations could directly map the MathML
mathvariant
attribute to the CSS text-transform
property.
Mathematical formulae rely on mathematical alphanumeric symbols
to provide specific meanings. For example, the Planck constant is denoted by
an italic h, vectors in physics are often written as bold variables, set of
numbers are represented by double-struck and Lie algebras by fraktur letters.
One can rely on properties such as font-style
or font-weight
to render
some of these symbols from basic alphanumeric characters but this is not
possible for others like fraktur, double-struck, calligraphic, etc
Unicode contains characters to describe this semantic information but they
are difficult to typeset with standard keyboard. It might also be
complicated for basic math parsers or renderers to properly inherit
mathvariant and perform transformations from the original characters. For
example in LaTeX,
$x + \mathfrak{\mathbb{\aleph+N} \sin \frac{2}{\alpha}}$
makes
x italic, N double-struck, 2 fraktur and all the other characters are
unchanged. Hence a CSS property similar to text-transform
to easily perform
transformation and inheritance would be helpful.
Most OpenType math fonts have glyphs to represent these characters but donâ€™t have associated italic/bold/bold-italic fonts. For generic fonts, the situation is actually the opposite: italic/bold/bold-italic fonts are available but not the corresponding mathematical alphanumeric symbols. It is tedious for math content generators or renderers to handle these different cases and decide some reasonable fallback, so a standardized approach is needed.
One important math typesetting convention is that single-character
identifiers are italic by default. Again, since OpenType math fonts have
italic mathematical alphanumeric symbols but no associated italic fonts,
using font-style: italic
does not provide the same visual rendering as
the equivalent mathematical alphanumeric symbols.
MathML defines a mathvariant
attribute to facilitate performing these
mathvariant transformations from the basic alphanumeric characters,
some kind of inheritance (e.g. like \mathfrak
above), automatic italic
on single-character <mi>
elements. Some fallback for things like italic
or bold are also suggested.
Mapping the mathvariant
attribute to some CSS property would allow
an implementation that is consistent with CSS inheritance or text-transform
.
text-transform
is implemented in all engines.mathvariant
attribute is implemented in Gecko and Stylo via an internal
CSS property.
It could be aligned with this specification with some refactoring and adjustments.mathvariant
attribute is partially implemented in WebKit using some custom
CSS-like inheritance and changing text rendering in token
elements but only works for single-character identifier (e.g. does not handle
<mi mathvariant="fraktur">sl</mi>
). Relying on a CSS property would
allow a cleaner and more complete implementation.text-transform
values. Gecko has layout tests for other edge cases
described in this specification.text-transform
valuesSee https://mathml-refresh.github.io/mathml-core/#new-text-transform-values
mathvariant
attributeSee https://mathml-refresh.github.io/mathml-core/#attribute-mathvariant