xmlstarlet (xmlstar.sf.net)
is the no-nonsense XML multitool that lets you write simple queries or
edits on the command line, avoids most of the stylesheet formal stuff,
and gives your <o/><o/>-looking eyes a moment of relief.
It's also a cranky minimalist tool which targets the 1.0 versions of
XPath / XSLT / EXSLT still widely used and, it seems, users with little
need for documentation.
This is an edited version of my personal notes on xmlstarlet with
worked examples -- knowledge gained as an outsider through use, trial
and error -- focusing on the select and edit commands and EXSLT.
It's not a tutorial or a FAQ, it requires a grasp of XML tools and
the POSIX shell.
Copyright is retained.
Available on GitHub Pages as
https://martin7th.github.io/xmlstarlet-notes/
https://martin7th.github.io/xmlstarlet-notes/news.html
Current version is 2023-08-15.