bracket
char bracket[3 + MB_LEN_MAX];
p->next = bracket;
n = wcrtomb(bracket, ch, &mbs);
bracket[n] = ']';
bracket[n + 1] = '\0';
p->end = bracket+n+1;
char bracket[4];
p->next = bracket;
p->end = bracket+3;
bracket[0] = '^';
bracket[1] = '\n';
bracket[2] = ']';
bracket[3] = '\0';
assert(p->next == bracket+3);
static int bracket(STR *);
if (bracket(s))