Syntax Coloring of XML Files

Files with the XML extension (*.xml) appear nicely formatted, but XML files with many other extensions (for example, *.dita) appear without any formatting. XML has become the universal standard for representing data, and I'm finding new extension types every day.
Currently, Source Preview Handler recognizes just five extensions as XML (*.xml, *.xsd, *.xsml, *.xsl, and *.kml).
  1. Is there a way that I can extend this list?
  2. Better yet, since all XML files contain the XML declaration (e.g., <?xml version="1.0" encoding="UTF-8" standalone="true"?>), could you update your code to use that to identify XML files?