Re: Why has inline-space length-specs?

[Tony Graham <tgraham@xxxxxxxxxxxxxxxx>]

At 22 Jul 1999 16:28 +0200, Peter Nilsson wrote:
 > while designing/implementing my DSSSL formatter, I came to a question
 > about inline spaces. The standard says (12.5.4.2):
 > (inline-space length-spec #!key min: max:)
 > 
 > (This procedure is used to construct an inline-space object.) All three
 > arguments are length-specs (i.e. may contain for instance (display-size)).
 > My concern is: why aren't the components of an inline-space just lengths?
 > The only flow objects that take inline-spaces as characteristic values
 > I've found are inline flow objects. But the display-size procedure may
 > only be called in the evaluation of a characteristic for a *displayed*
 > flow object. So isn't it useless to have length-specs here?

Looking at Section 12.5.2, I can find two features of length-specs
that would make them useful in inline-space declarations.  Firstly, a
length-spec "specifies a length as a linear combination of other
lengths that may not be currently known", and secondly you can compute
a value for the length-spec based on something else.  For example:

   escapement-space-before: (inline-space (* 2 (actual-font-size))
                                          min: (* 1.8 (actual-font-size))
                                          max: (* 2.2 (actual-font-size)))

These length-specs, and the resulting inline-space, are computed from
the value of another characteristic.

(Actually, I could be just computing lengths, but you get the idea.)

Regards,


Tony Graham
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