length-spec vs. length for characteristics

[Tony Graham <tgraham@xxxxxxxxxxxxxxxx>]

The reasons for and consequences of differentiating between a
length-spec and a length as the value of a characteristic elude me.
Can anyone explain?

Section 12.5.2 states:

"An object of type length-spec specifies a length as a linear
combination of other lengths that may not be currently known.
Whenever a value of type length-spec is required, a length (a quantity
of dimension 1) may always be used."

Does this mean that only for characteristics with a length-spec value,
I can use display-size (also introduced in 12.5.2) to return a
length-spec that I can use when setting the value of the
characteristic?  What other ways are there for arriving at a
length-spec instead of a plain old length?

For that matter, what specifies the "value flow object" for
display-size?

I was started on this tack by looking at the following characteristics
of the box flow object class and their values:

	box-corner-radius	length-spec
	box-size-before		length
	box-size-after		length
	start-indent		length-spec
	end-indent		length-spec

For example, why is box-corner-radius a length-spec and
box-size-before a length?

Regards,


Tony Graham
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Tony Graham, Consultant
Mulberry Technologies, Inc.                         Phone: 301-231-6931
6010 Executive Blvd., Suite 608                     Fax:   301-231-6935
Rockville, MD USA 20852                e-mail: tgraham@xxxxxxxxxxxxxxxx
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