PREV_BEGBUF_CONSTRAINT  226 maint/gnulib/lib/regex_internal.h   BUF_FIRST = PREV_BEGBUF_CONSTRAINT,
PREV_BEGBUF_CONSTRAINT  514 maint/gnulib/lib/regex_internal.h   || ((constraint & PREV_BEGBUF_CONSTRAINT) && !IS_BEGBUF_CONTEXT (context)))