regexp.go
func NewRegexpPath(pattern string) (*RegexpPath, error) {
	r, err := CompileRegexp(pattern)
	if err != nil {
		return nil, err
	}
	return &RegexpPath{*r}, nil
}
func NewRegexpPath(pattern string) (*RegexpPath, error) {
	r, err := CompileRegexp(pattern)
	if err != nil {
		return nil, err
	}
	return &RegexpPath{*r}, nil
}
// RegexpPath -----------------------------------------------------------------
// NewRegexpPath returns a regexp matcher for the given URL path pattern.