Specified, Computed, Used, Actual values
Emanuele D'Arrigo
newbie here...
I'm a bit puzzled about the implementation details of the CSS standard
and I'm looking at Mozilla in search of inspiration.
In theory, Specified, Computed, Used and Actual values are relatively
clear. The specified value comes from the content model/style sheet or
is a default value, computed is an absolutized or inherited version of
the specified value, used is the computed value in light of the actual
layout of the document and the actual value deals with limitations of
the output device or media.
But questions quickly multiply when trying to implement those concepts
into a concrete class handling CSS properties. I.e. is a property such
as "width" actually stored somewhere in four related copies, one for
each type of value? I.e. assuming an element such as
<div style="width:30%">aTest</div>
are there four variables stored somewhere and set as
specified = "30%"
computed = "200px"
used = 180.47
actual = 180
or is only the specified value stored, while the other three values
are calculated on the fly when and if they are needed?
If they are stored in four variables, would I be correct to say that a
change in the content model or in the stylesheet triggers the
recalculation of all four values while a change in, say, the size of
the browser window only triggers the recalculation of computed, used
and actual values? Or am I oversimplifying?
Manu