I\'ve seen this syntax several places (eg, here):
xmllint --xpath \'/plist/array/string/text()\' tmp.xml, used to query a particular XML node using an x
xmllint --xpath \'/plist/array/string/text()\' tmp.xml
Ah, yep, must've been an issue with an outdated version of libxml2.
libxml2
Updating libxml2 (to v2.7.8) via macports seems to have fixed the problem.
v2.7.8