Make <rp> available inside <sup> and <sub>

[Crissov]

Superscript text is often used for exponents, e<sup>i&InvisibleTimes;&pi;</sup> or 10<sup>9</sup>. This semantic information is lost when copying to plain text: eiπ, 109. When ruby annotation markup was added to HTML, it came with a dedicated element for textual fallback: <rp>. Can we reuse that for superscript and subscript text?

e<sup><rp>^(</rp>i&InvisibleTimes;&pi;<rp>)</rp></sup>
10<sup><rp>**</rp>9</sup>
C<sub><rp>_</rp>6</sub>H <sub><rp>_(</rp>12<rp>)</rp></sup> O<sub><rp>_</rp>6</sup>
<abbr title="madame">M<sup>me<rp>.</rp></sup></abbr>

A quick test in browsers suggests that some (e.g. Chrome, Edge, Firefox) drop the content of the <rp> element inside <sub> or <sup>, which is good, but they don’t copy the hidden text for plain-text pasting, which is very bad. Others (e.g. Safari) display (and, of course, copy) the contents, which means that some CSS would be required for them.

[spixi]

<rp> is only allowed as child of <ruby>. In this case the behavior is undefined. We had a discussion on the Unicode mailgroup and I actually like this idea. The problem is that the semantic part of <sub> and <sup> gets lost if you copy rendered HTML from your browser to an application which only knows plaintext. E. g. 2<sup>3</sup> becomes 23. The Unicode replacement characters like ³ are not sufficient, because they cannot cover nested super- and subscripts, for example.

[annevk]

That seems like a bug in Safari, rp is supposed to be display:none per the Rendering section.

[r12a]

Can we please stop trying to use ruby markup as a general can-opener. HTML is a language based on semantics. What you are marking up here are not ruby parentheses. Is there no solution for this in MathML?

[Crissov]

I’d have no problem with a new dedicated element, but <rp> already has the proper semantics, it’s just restricted to a different context at the moment.

[spixi]

I thought about the topic and see that reusing <rp> would break downwards-compatibility. <rp>, <noscript> and the custom elements are specifically designed, with the thought in mind, that legacy browsers ignore unknown tags and treat them similar to <span>. Given that there is a browser which knows <sup>, but not <rp>, the expression e<sup><rp>^(</rp>i&InvisibleTimes;&pi;<rp>)</rp></sup> would be rendered e^{^(i⁢π)} instead of e^i⁢π or e^(i⁢π).

[spixi]

But what about a <nomath> element? You could write: <math alttext="e^(i⁢π)"><mrow><msup><mi>e</mi><mrow><mi>i</mi><mi>π</mi></mrow></msup><mrow></math><nomath> (e^(i⁢π))</nomath> to provide a copy-friendly version of your formula.