Application for extracting XML tags from a document

Solution 1:

~~xml2~~ xml2

  <foo.xml xml2 | cut -d= -f1 | sort -u

  <foo.xml xml2 | cut -d= -f1 | sort -u | 2xml

etc

omit the sort -u if you are interested in repetitions & duplicates.

If you don't want to see attributes

  <foo.xml xml2 | grep -v @ | cut -d= -f1 | sort -u | 2xml

If you want to use xml2 on Windows you'll probably need Cygwin or unxutils or gnuwin32 etc.