xmllint apparently does not catch invalid attribute values as defined in relaxng schema.
$ xmllint --noout --relaxng schema/ms-transcription.rng ms-xml/tc/tc_p001r_preTEI.xml ms-xml/tc/tc_p001r_preTEI.xml validates jing does:
$ java -jar ~/Dropbox/xml/tools/jing/bin/jing.jar schema/ms-transcription.rng ms-xml/tc/tc_p001r_preTEI.xml /Users/terry/Github/m-k-manuscript-data/ms-xml/tc/tc_p001r_preTEI.xml:10:38: error: value of attribute "render" is invalid; must be equal to "full", "tall" or "wide"
this is still a bug in xmllint (not catching invalid attribute values), so this should be considered
https://relaxng.org/jclark/jing.html (jing is the validator created by RelaxNG dude)