\a is equivalent to
[A-Za-z] so it matches only non-accented letters.
I know of
[=name-of-equivalence-class=], so I can clearly use something like
\(\a\|[[=a=][=e=][=i=][=o=][=u=]]\), but I was wondering whether there was a more fundamental solution, such as an option to automatically match every element of the equivalance class for each character in the pattern.
I haven't found anything in