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htmlpurifier/docs/ref-css-length.txt
Edward Z. Yang 9dd7c8c7dd Add reference document on CSS lengths.
git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1264 48356398-32a2-884e-a903-53898d9a118a
2007-06-27 23:49:50 +00:00

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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).