REG_STARTEND
#define REG_BACKR (REG_STARTEND << 1)
errcode = regexec(pre, str, 1, &pmatch, REG_STARTEND);
REG_STARTEND) != 0)
REG_STARTEND) == 0)
nomatch ? 0 : maxnsub + 1, match, eflags | REG_STARTEND);
if (regexec(&rgx, bfr, 0, &pmatch, REG_STARTEND) == 0)