DOCBOOK-APPS: Why Specify "colwidth" Attribute for XSL Style Sheets?

Hi!

I'm curious why it's necessary to specify the colwidth attribute in
colspec elements when working with the DocBook XSL style sheets. When
using the DSSSL style sheets instead this is not required. Why are
colspecs treated differently in DSSSL and XSL style sheets?

Thanks in advance for any hints!

Greetings,

	Holger