#295 Custom text role with inheritence on math role should respect additional class

[Oleksandr Gavenko]

From: Tom Roche
Subject: styling a replacement
Archived-At: http://permalink.gmane.org/gmane.text.docutils.user/7512

asked about styling replacement. He uses chemical formula H2O and want "2" be subscript and all text be emphasised.

This already do :math: role / directive.

I try:

.. role:: chem(math)
:class: chem

This is :chem:H_2O.

but unfortunately get:

CO₂

I can't see additional class "chem". It would be very heplful to distinguish mathematical and chemical formulas in resulted HTML via custom additional style.

See original reference that suggest such usage: http://docutils.sourceforge.net/docs/ref/rst/directives.html#custom-interpreted-text-roles

[Dmitry Shachnev]

FWIW using math for chemical formulas is unnecessary — they can be rendered using plain HTML while the math role will usually result in being rendered with something like MathJax.

You can write H₂0 with the help of this tip (looks like the author of docutils-user post did exactly that).

[Günter Milde]

The problem is, that italic subscripts are another form of nested inline markup and require a custom role with matching CSS styling rule. So, while not impossible, the substitution-approach becomes quite complicated (see attachment).
However, as David Goodger suggested this special case is better solved using Unicode characters for the subscript 2.

[Günter Milde]

While I do not recommend using :math: for chemical formulas, the request for class-inheritance of a custom role is valid.

This is fixed now, thanks for the bug report.