XMLStarlet Toolkit: Display element structure of XML document
Usage: PROG el [<options>] <xml-file>
where
  <xml-file> - input XML document file name (stdin is used if missing)
  <options> is one of:
  -a    - show attributes as well
  -v    - show attributes and their values
  -u    - print out sorted unique lines
  -d<n> - print out sorted unique lines up to depth <n>