Tree data - sgml/signature GitHub Wiki
https://www.xml.com/articles/2017/11/05/oasis-genericode-tables/
http://monet.nag.co.uk/xq2xml/#s3
https://odetocode.com/blogs/scott/archive/2009/06/05/from-linq-to-xpath-and-back-again.aspx
http://www.4guysfromrolla.com/articles/062310-1.aspx
https://www.slideshare.net/AnandRaj5/understanding-linq-13726724
http://www.dtic.mil/dtic/tr/fulltext/u2/a602751.pdf
http://www.dtic.mil/dtic/tr/fulltext/u2/1016360.pdf
http://www.d-m-s.co.nz/serv_xmlval.htm
https://reference.niem.gov/niem/specification/code-lists/1.0/niem-code-lists-1.0-2016-06-20.html