const regexp/syntax.PerlX

7 uses

	regexp/syntax (current package)
		parse.go#L64: 	PerlX                           // allow Perl extensions
		parse.go#L71: 	Perl        = ClassNL | OneLine | PerlX | UnicodeGroups // as close to Perl as possible
		parse.go#L409: 	if p.flags&PerlX != 0 {
		parse.go#L937: 			if p.flags&PerlX != 0 && len(t) >= 2 && t[1] == '?' {
		parse.go#L1018: 			if p.flags&PerlX != 0 && len(t) >= 2 {
		parse.go#L1582: 	if p.flags&PerlX == 0 || len(s) < 2 || s[0] != '\\' {
		parse.go#L1754: 		if t != "" && t[0] == '-' && p.flags&PerlX == 0 && !first && (len(t) == 1 || t[1] != ']') {