want to know if something is a valid NCName? easy! just do

/self::node()[exsldyn:evaluate(concat('not(self::exsldyn:', $thing, ')'))]

XSLT 1.0 + EXSLT is a constant exercise in things you probably weren’t intended to be able to do but nevertheless can

this probably actually needs a touch of hardening (making sure $thing does not contain a '[' or '/', or else you could run into serious issues) but

/self::node()[translate(normalize-space($thing), ' /([,*', '')=string($thing) and exsldyn:evaluate(concat('not(self::exsldyn:', $thing, ')'))]

i think is safe

here is a shell command you can run to test whether the value of MAYBE_NCNAME is an ncname or not; returns exit status 0 if it is and 1 otherwise

printf '%s\n' '<transform xmlns="http://www.w3.org/1999/XSL/Transform" xmlns:exsldyn="http://exslt.org/dynamic" version="1.0"><param name="thing"/><template match="/"><choose><when test="/self::node()[translate(normalize-space($thing), &quot; /([,*&quot;, &quot;&quot;)=string($thing) and exsldyn:evaluate(concat(&quot;not(self::exsldyn:&quot;, $thing, &quot;)&quot;))]">ok</when><otherwise>ng</otherwise></choose></template></transform>' | xsltproc --stringparam thing "${MAYBE_NCNAME}" --html --novalid - /dev/null 2>/dev/null | grep -F -q -x 'ok'

this might be the easiest portableish way of doing this and that is a condemnation of the current state of computing on Posix

@Lady Can't do it in sed?

@aschmitz you could do it in sed but i’m not sure the regex would be shorter and personally i would rather not worry that i may have a bug in my regular expression

@aschmitz (grep actually would probably be more appropriate but same difference)

@aschmitz (and if we want to be fully honest, unicode support in grep/sed is dicey so the answer might actually be no)

@Lady At least cross-platform, I guess.