[whatwg] Physical quantities: <var> or <i>?

[Jukka K. Korpela]

Looking at the nice summary (with examples) of text-level markup at
http://www.whatwg.org/specs/web-apps/current-work/multipage/text-level-semantics.html#usage-summary
I started wondering why there is no example of markup for symbols of 
physical quantities. The descriptions of individual elements or their 
examples don't seem to say anything about this either.

So what markup should we use for E = mc², given that by the applicable 
standards, E, M, and c should appear in italics and the other characters as 
normal (upright)?

Physical quantities surely satisfy the requirement that "typical typographic 
presentation is italicized" in the following, and they are to be offset from 
the normal prose, but why aren't they mentioned in the fairly long list of 
examples then:

"The i element represents a span of text in an alternate voice or mood, or 
otherwise offset from the normal prose, such as a taxonomic designation, a 
technical term, an idiomatic phrase from another language, a thought, a ship 
name in Western texts, or some other prose whose typical typographic 
presentation is italicized."
http://www.whatwg.org/specs/web-apps/current-work/multipage/text-level-semantics.html#the-i-element

(As an aside, the wording "a taxonomic designation" is too broad, as by 
biological nomenclature rules, genus and species names are to be italiced 
but higher taxons, e.g. family names, like Canidae, must not. Besides, e.g. 
an English name of a species is taxonomic too... So "scientific names of 
organisms" would be a better formulation.)

But the i element should obviously be used in the absence of a more semantic 
element; e.g., not for expressions that fall into the scope of use of the 
cite element.

Should we consider the var element as covering physical quantities too? 
After all, they can be regarded as variables in a broad sense, as symbols 
that denote different values in different situations. However, <var>c</var> 
would be odd, wouldn't it, since the symbol denotes a universal constant of 
nature.

So I would guess that <i>E</i> = <i>m</i><i>c</i>² is the way to go.

I think an example like this, or the addition of physical quantities into 
the list of examples, or both, would be the semantics and intended use of 
elements somewhat clearer.

-- 
Yucca, http://www.cs.tut.fi/~jkorpela/