[Bug 3512] Implement font-stretch property

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--- Comment #48 from Zack Weinberg   2008-06-04 17:30:58 PDT ---
The problem with a single-number coding scheme like "501 = normal + 1 step
(wider/bolder)" is that wider/narrower, like bolder/lighter, are required to
make a change if they can.  So, consider

<span style="font-stretch: normal">a
 <span style="font-stretch: wider">b
  <span style="font-stretch: narrower">c
</span></span></span>

Suppose that the font family for this entire thing has two widths: normal and
condensed.  (Pretty common.) Then the spec says "a" and "b" should be rendered
at normal width, and "c" at condensed width.  But with a single-number scheme,
the style for "c" is indistinguishable from the style for "a".