Hello,

It might be handy to have a check to see if a value is any quark, for
"make safe" code. So far, I've ended up with:

\def_new:Npn \if_quark:NT #1 {
  \exp_after:NN \exp_after:NN \exp_after:NN \if_quark:w
    \exp_after:NN \token_to_string:N #1 \q_stop
}

\def_new:Npn \if_quark:wT #1#2#3\q_stop {
 \int_compare:nNnT {\char_value_uccode:n{#2}} = {`Q}
}

which seems to work but I'm worried may not be suitable more generally.
 Any ideas?
-- 
Joseph Wright