Jim Meyering <jim@meyering.net> wrote:
> dfa.c's match_mb_charset function *is* used, e.g., in a
> command like this one:
> 
>   printf '\0' |src/grep -aE '^\s?$'

Wow, just it isn't good.  I think that behavior of `fails' should be
same as of `trans' except `fails' checks accepted conditions, including
following part.  match_mb_charset() should be avoided as far as possible,
as it doesn't support collating symbols and equivalence classes.

>               /* Falling back to the glibc matcher in this case gives
>                  better performance (up to 25% better on [a-z], for
>                  example) and enables support for collating symbols and
>                  equivalence classes.  */
>               if (d->states[s].has_mbcset && backref)
>                 {
>                   *backref = 1;
>                   goto done;
>                 }