
CSS Length Reference
  To bound, or not to bound, that is the question

It's quite a reasonable request, really, and it's already been implemented
for HTML.  That is, length bounding.  It makes little sense to let users
define text blocks that have a font-size of 63,360 inches (that's a mile,
by the way) or a width of forty-fold the parent container.

But it's a little more complicated then that. There are multiple units
one can use, and we have to a little unit conversion to get things working.
Here's what we have:

Absolute:
    1 in ~= 2.54 cm
    1 cm = 10 mm
    1 pt = 1/72 in
    1 pc = 12 pt

Relative:
    1 em ~= 10.0667 px
    1 ex ~= 0.5 em, though Mozilla Firefox says 1 ex = 6px
    1 px ~= 1 pt

Watch out: font-sizes can also be nested to get successively larger 
(although I do not relish having to keep track of context font-sizes,
this may be necessary, especially for some of the more advanced features
for preventing things like white on white).

Add reference document on CSS lengths.
Add reference document on CSS lengths.

git-svn-id: 25f448894bd6eb0cddf10ded73b4f5a7ea3203f3@1264 48356398-32a2-884e-a903-53898d9a118a
