Hello all,

One question occurs to me about xparse "processors". I've provided one
that splits on a comma, \xparse_process_comma_split:n. I wonder what the
behaviour of this type of function should be if the input is not of the
correct form. At the moment, if you apply a processor to an optional
argument and no value is given, the special \NoValue token is left
alone.  The normal behaviour for this function is:

\xparse_process_comma_split:n { 1,2 } => {1} {2}

but what should happen with

\xparse_process_comma_split:n { 12 }

A the moment you get "{12} \NoValue" so that exactly two results are
returned. Should you get perhaps just \NoValue, or something else?
Joseph Wright