[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.   `._.-(,_..'--(,_..'`-.;.'

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