T("    u	standard unspecified behavior -- errors not counted\n");
T("    v	REG_CLASS_ESCAPE	\\ special inside [...]\n");
T("    w	REG_NOSUB		no subexpression match array\n");
T("    x	REG_LENIENT		let some errors slide\n");
T("    y	REG_LEFT		regexec() implicit ^...\n");
T("    z	REG_NULL		NULL subexpressions ok\n");
T("    $	                        expand C \\c escapes in fields 2 and 3\n");

		strflags = iflags
	}
	sub = out

	// Round 2: Factor out common simple prefixes,
	// just the first piece of each concatenation.
	// This will be good enough a lot of the time.
	//
	// Complex subexpressions (e.g. involving quantifiers)
	// are not safe to factor because that collapses their
	// distinct paths through the automaton, which affects
	// correctness in some cases.
	start = 0
	out = sub[:0]