Have you taken a look at the XPath documentation resources?
- The primary manual for ConfD is the YANG and NETCONF RFC pointing to W3C standard. The ConfD UG complements the YANG and NETCONF RFCs. See:
https://tools.ietf.org/html/rfc7950#ref-XPATH
https://tools.ietf.org/html/rfc6241#section-8.9.1 - See also ConfD UG under “NETCONF Server” “Capabilities” “:xpath”
- Including the link to the xpath 1.0 standard in those documents (for example “4.1 Node Set Functions” can be handy sometimes)
https://www.w3.org/TR/1999/REC-xpath-19991116/ - Then there are ConfD YANG extensions regarding xpath in the tailf_yang_extensions man page section “XPATH FUNCTIONS”