//     A	REG_AUGMENTED		ARE	(egrep with negation)
		//     S	REG_SHELL		SRE	(sh glob)
		//     K	REG_SHELL|REG_AUGMENTED	KRE	(ksh glob)
		//     L	REG_LITERAL		LRE	(fgrep)
		//
		//     a	REG_LEFT|REG_RIGHT	implicit ^...$
		//     b	REG_NOTBOL		lhs does not match ^
		//     c	REG_COMMENT		ignore space and #...\n
		//     d	REG_SHELL_DOT		explicit leading . match
		//     e	REG_NOTEOL		rhs does not match $