> This problem is known as "grouping": you'll find it in the index of any
XSLT
> book under that name, or at http://www.jenitennison.com/xslt/grouping.
It's
> easy in XSLT 2.0 using <xsl:for-each-group>, but a little tricky in XSLT
1.0.

Great resource - thanks Michael!