[whatwg] Editorial: 3.10.18. The |sup| and |sub| elements

Ian Hickson ian at hixie.ch
Tue Dec 11 22:19:57 PST 2007

```On Wed, 1 Nov 2006, Christoph Päper wrote:
>
> The second to last example should probably better read:
>
>   <var>E</var> = <var>m</var> · <var>c<var><sup>2</sup>
>
> or maybe, as the speed of light is a constant,
>
>   <var>E</var> = <var>m</var> · c<sup>2</sup>.

If you are suggesting adding the multiplication sign, I disagree; the
equation is always just written E=mc^2 in my experience.

On Sat, 4 Nov 2006, Matthew Paul Thomas wrote:
>
> Is that equation ever legitimately rendered (in physics textbooks etc)
> with the "m" in a different style from the "c"? If not, perhaps the
> definition of <var> needs to be expanded to include physical constants.

On Mon, 6 Nov 2006, David Walbert wrote:
>
> No, constants and variables are presented identically in equations. The
> student simply is expected to know whether they are constants or not.
> This requires some context, but the equation makes sense only with
> context anyway. If I understand the draft standards correctly the var
> would be defined by a prior dfn element, and that is where one would
> note (if one believed it necessary) that the speed of light was
> constant.
>
> If that equation is considered only algebraically, then E, m, and c are
> treated identically anyway -- there is no difference in how you handle
> them mathematically.
>
> Is var really not meant to include constants represented algebraically?
> That would take semantic markup to a level that seems to me frankly
> silly.

I agree, as does the spec. Constants in physics are variables in
mathematics, and the spec explicitly refers to variables in the
mathematical sense.

--
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
```