STK_ALT           532 regexec.c        stk->type = STK_ALT;\
STK_ALT           570 regexec.c      #define STACK_PUSH_ALT(pat,s,sprev)     STACK_PUSH(STK_ALT,pat,s,sprev)
STK_ALT          1298 regexec.c        STACK_PUSH_ENSURED(STK_ALT, (UChar *)FinishCode);  /* bottom stack */