I am the first (and still the only one) to hold all of these: the gold badge in XSLT, the gold badge in XML and the gold badge in XPath.

Some of the more interesting things I've been doing can be found via these links:

     Training course on "XSLT 2 and 1 Foundations", -- 12 modules, 8:45 hours
     the FXSL page,
     my Finger Tree implementation in C#
     My Original XPath Visualizer hosted by Lars Huttar
     the Extreme Markup Conf. presentation on FXSL 2.0
     My Balisage 2013 paper "Programming in XPath 3.0",
      and the PPT presentation
     My Blog
     Follow me on Twitter