Mark asked:

"Is there a significant difference between xsl:import and xsl:include
worth learning?"

The only difference between xsl:import and xsl:include is that
xsl:import must be the very first child of xsl:stylesheet.

This means that if the importing stylesheet has templates that matches
with same priority as the templates in the imported stylesheet, the
templates in the importing stylesheet are sure to win out because they
are after the templates in the imported stylesheet.

That is you never really need to use xsl:import. If you make sure that
an xsl:include is the very first child of xsl:stylesheet, it works
exactly as if xsl:import had been used.

Michael Kay
Saxonica