DOCBOOK-APPS: Normalizing spaces?

Can someone give me a quick pointer to how the effect of taking an 
arbitrary number of whitespace characters in the document and normalizing 
them into a single space character is achieved?  The specific example is 
the treatment of whitespace in a <para> (and other) element in the DocBook 
DTD processed with the Modular DSSSL Style Sheets.

I am working in SGML and processing with DSSSL, if that was not obvious.

Mark B. Wroth
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