Re: Units, font sizing, and zoom suggestion for CSS 3

> Units, font sizing, and zoom suggestion for CSS 3
> Absolute length units (the parenthesised ones may be ignored):

Further extensions are pointless as absolute lengths are inappropriate
in most cases.
> 
>         µm - micrometer (spelling: use either U+03BC (preferred) or
>                 U+00B5 as the first letter; the spelling with U+339B
>                 should be deprecated, if at all allowed).
Not useful - no property requires a unit that small.
>         mm - millimeter (preferred unit for absolute font sizing; the
>                 spelling with U+339C should be deprecated, if at all
> allowed).
> 
>         cm - centimeter (the spelling with U+339D should be deprecated,
>                 if at all allowed).
> 
>         dm - decimeter.
Not useful - just use 10cm
> 
>         pt - pica point, about 0.3515 mm (i.e. 351.5 µm); should be
>                 deprecated.
The definition as 1/72 inch is fine. There is no need to change to
metric.
> 
>         (bpt - big pica point, about 0.3528 mm (i.e. 352.8 µm), 0.4 %
>                 bigger than pt; should be deprecated, if at all allowed.)
See comments regarding extensions as being pointless - you can always
use cm or inch if you really must.
> 
>         dd - Didôt point, 0.376 mm (i.e. 376 µm), 7.0 % bigger than
>                 pt, 6.6 % bigger than bpt; commonly used in traditional
>                 European (non-British) typography; new to CSS but should
>                 be deprecated.
> 
See comments regarding extensions as being pointless - you can always
use cm or inch if you really must.
>         pc - pica, about 4.2175 mm (i.e. 4 217. 5 µm); should be deprecated.
The definition as 1/12 inch is fine. There is no need to change to
metric.
> 
>         (bpc - big pica, 12 pt, about 4.233 mm (i.e. 4 233 µm);
>                 should be deprecated, if at all allowed.)
See comments regarding extensions as being pointless - you can always
use cm or inch if you really must.
> 
>         cc - cicero, 12 dd, 4.512 mm (i.e. 4 512 µm); commonly used in
>                 traditional European (non-British) typography; new to CSS
>                 but should be deprecated.
> 
See comments regarding extensions as being pointless - you can always
use cm or inch if you really must.
>         in - inch, 2.54 cm (i.e. 25 400 µm; exactly); should be deprecated.
> 
> Relative length units (the parenthesised one may be ignored):
More useful.
[snipped - no comment]
>         em - width(!) of a capital M in the current font and size;
>                 this is the historically correct definition of em,
>                 and the definition of em used by TeX; if there is no
>                 M in the font, a suitable approximation is calculated.
This is a bad idea - it would ruin all old implementations. 

My wem suggestion is backward-compatible
> 
>         (en - half an em. (Not necessarily the width of an N.))
Superfluous, just divide your wems by 2.
> 
>         tmu - 1/18 em, TeX 'math unit' (not so wisely called 'mu'
>                 there).
Superfluous; however less so as /18 is less easily done mentally.
> 
>         px - (see the description in the CSS 2 specification and
>                 the note about zoom below; in the unusual (nowadays)
>                 event that the screen has very low resolution, 1 px
>                 may be significantly smaller than one pixel).
Depending of course on the viewing distance.
> 

> Font size setting (font-ex-size is a suggested new attribute):
> 
>         font-size - sets (or changes) the Åp height, which is
>                 maintained through typeface changes; the ex, em, (en),
>                 and tmu may vary depending on typeface.
No changes to well-established properties please.
> 
>         font-ex-size - sets (or changes) the ex height, which is
>                 maintained through typeface changes; the Åp, em, (en),
>                 and tmu may vary depending on typeface; even though
>                 the Åp height may change through typeface changes,
>                 the baseline separation does not change with it.
This I like very much.

> Global zoom:
CSS 2 specifies that zooming is left to UAs; I see no problem with this.