[css3-text] computed values for <length>s

(I'm just choosing a couple of properties from css3-text as an example.)

The "Computed value" line for the tab-size property definition says 
"specified value".  css3-values however says that "Child elements do not 
inherit the relative values as specified for their parent; they inherit 
the computed values."  Does css3-values override the tab-size definition 
here?  Or does "specified value" mean "the same value that was specified 
but with all of the computed value changes that are required elsewhere"?

This is in contrast to word-spacing, which says "as specified, except 
with <length> values computed to absolute lengths", so it's explicitly 
calling out the computation of <length>s.

Also, when it is stated that <length>s are converted into absolute 
lengths, does that mean any of the absolute length units are allowed 
(like cm)?


I ask because I wonder whether property definitions in SVG need to 
mention <length> computation explicitly in their "Computed value" lines, 
or whether this will happen automatically if I just state "as 
specified".  And if it doesn't happen automatically, whether all SVG 
properties ought to be computing <length>s down to absolute lengths.

Thanks,

Cameron