RE: What's an em

Well, the (non)-realism of the CCS2 font-size-adjust example aside for
a moment:

Assume the (lowercase dominated) headings are asked (by the page author)
to be of x-height 7 mm in Flemish Script, the body text (lowercase
dominated) to be of x-height 3.5 mm Verdana.  Whatever font substitutions
are done (keeping the asked-for x-heights to a reasonable degree), one
would still get a proper percieved size difference between the heading
and the body text.  Right? Or??? An invariant you would NOT get if the
heading and body sizes were asked for in "point sizes" for some unknown
square.  Right?  'Definiteveness' is a non-issue when the text is hard
to read, or even unreadable.

Please read my suggestion again before entangling everyone in strange
calculations that have nothing to do with the suggestion at hand.

But as I said before, my issue is not with extreme typefaces, where 
some odd (but hopefully not too odd) effects may occur, but with
ordinary "every-day" typefaces.  So even if it is not perfect, *some*
adjustment to get *near* size invariance is better than complete
non-invariance.  Which does give problems NOW, when different systems
do different font substitutions, and the author might have no idea
what font substitutions are done (and would not care to test them all,
even if he/she did).  


		Kind regards
		/kent k


> -----Original Message-----
> From: Clive Bruton [mailto:clive@typonaut.demon.co.uk]
> Sent: Wednesday, February 02, 2000 4:38 PM
> To: www-font@w3.org
> Cc: www-font@w3.org; www-style@w3.org
> Subject: Re: What's an em
> 
> 
> Erik van der Poel wrote at 02/02/00 06:15
> 
> >My understanding is that the "perceived" size is so dependent on the
> >x-height, that the heading wouldn't *look* smaller than 
> continuous text
> >on the same page.
> 
> Let me give an example, using the "oh so realistic" comparisons 
> previously cited in the CSS2 spec. Compare the font size 
> adjust at the 
> extremes: Verdana and Flemish Script.
> 
>      If I set a heading in 24pt Flemish Script, but the
>      user decides that they really want everything in Verdana
>      then the font size adjust mechanism will scale the "real"
>      size by 0.5 to 12pt to match the "perceived" font size.
> 
> Correct?
> 
> Isn't it reasonable to assume that continuous text on the 
> same page might 
> be set at 12pt? Thus the heading would be indistinguishable 
> in size from 
> the text. Perhaps more realistic is that a heading might be 
> 18pt, thus 
> with font size adjust it would scale to 9pt - smaller than the text.
> 
> Perhaps other more realistic outcomes are that a large 
> x-height sans like 
> Verdana is being used in continuous text, or as sub heads, to 
> match the 
> "perceived" size of the text, thus in the designers intended 
> style the 
> sans is set perhaps 1pt smaller than the text (this is quite common).
> 
> But the user says, "I want Times", thus the sans sub heads 
> and emphasis 
> in text get scaled by 1.26 the size of the text, ie perhaps 
> (10pt - 1pt) 
> * 1.26 = 11.34 - bigger than the continuous text, which wasn't the 
> designers intention either.
> 
> Perceived size isn't just a factor of x-height, it's a factor 
> of design, 
> ie relationships between x, cap, ascender and descender.
> 
> >
> >> Do you want to give an example of where you think knowing 
> the x-height
> >> might be something useful?
> >
> >Suppose the document author chose Verdana at a certain size. 
> Now suppose
> >the reader doesn't have Verdana...
> 
> I think then the document creator should have used 
> alternatives, some of 
> which were guaranteed to be on the system. In continuous text I think 
> document creators generally specify the default sytem fonts 
> as they can 
> be assumed to be available. They try to represent something that all 
> users will see, rather than what their real preference would be.
> 
> 
> -- Clive
>