HTML and CSS Reference
In-Depth Information
8.4.1.1. Keyword property values
A property may have a
keyword
value that expresses action or dimen-
sion. For instance, the effects of
underline
and
line-through
are obvi-
ous property values. And you express property dimensions with such
keywords as
small
and
xx-large
. Some keywords are even relational:
bolder
, for instance, is an acceptable value for the
font-weight
property.
Keyword values are not case sensitive:
Underline, UNDERLINE
, and
under-
line
are all acceptable keyword values.
8.4.1.2. Length property values
So-called
length
values (a term taken from the CSS2 standard) explicitly
set the size of a property. They are numbers, some with decimals, too.
Length values may have a leading + or - sign to indicate that the value
is to be added to or subtracted from the current value of the property.
Length values must be followed immediately by a two-letter unit abbre-
viation, with no intervening spaces.
There are three kinds of length-value units: relative, pixels, and abso-
lute. Relative units specify a size that is relative to the size of some oth-
er property of the content. Currently, there are only two relative units:
em
, which is the width of the lowercase letter "m" in the current font;
and x-height, abbreviated
ex
, which is the height of the letter "x" in the
current font.
Pixels are the tiny dots of colored light that make up the onscreen text
and images on a computer monitor or TV image. The pixels unit, abbre-
viated
px
, is equal to the minute size of 1 pixel, so you may express the
size of some properties by how many pixels across or down they run.
Absolute property value units are more familiar to us all. They include
inches (
in
), centimeters (
cm
), millimeters (
mm
), points (
pt
;
1
/
72
of an
inch), and picas (
pc
; 12 points).
