xmllint is a wrapper over xmllint from libxml2-utils.

The goal is to implement --xpath switch for very old version of xmllint and to have newlines delimited output. (Unlike version < 2.9.9).
Require bash and... xmllint

Example with wrapper:

$ xmllint --html --xpath '//a/@href' http://www.w3.org/
href="/"
href="/standards/"
href="/participate/"
(...)

Example without wrapper:

$ xmllint --html --xpath '//a/@href' http://www.w3.org/
 href="/" href="/standards/" href="/participate/" href="/Consortium/membership"

Another approach

Install a subsystem: https://serverfault.com/a/1022826/120473

edit 20180923: for newline delimited output, bug fixed upstream in libxml2-utils v2.9.9, check

• https://gitlab.gnome.org/GNOME/libxml2/commit/da35eeae5b92b88d8ebdb64b4b327ac1c2cf1bce
• discussion: https://gitlab.gnome.org/GNOME/libxml2/-/merge_requests/8
• https://mail.gnome.org/archives/xml/2018-March/msg00008.html
• https://bugzilla.gnome.org/show_bug.cgi?id=740827