b += 0x20
		}
		if a != b {
			return false
		}
	}
	return true
}

// isDomainName checks if a string is a presentation-format domain name
// (currently restricted to hostname-compatible "preferred name" LDH labels and
// SRV-like "underscore labels"; see golang.org/issue/12421).
//
// isDomainName should be an internal detail,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:

//     the requirements of Section 3 are satisfied.  Note that even LTR
//     labels and pure ASCII labels have to be tested.
//
//  o  In a domain name consisting of only LDH labels (as defined in the
//     Definitions document [RFC5890]) and labels that satisfy the rule,
//     the requirements of Section 3 are satisfied as long as a label
//     that starts with an ASCII digit does not come after a

	return 'A' <= c && c <= 'F' || 'a' <= c && c <= 'f' || '0' <= c && c <= '9'
}

func isDigit(c byte) bool {
	return '0' <= c && c <= '9'
}

func skipDomainElem(s string) (int, bool) {
	// String of LDH, up to 63 in length, with LetterDigit
	// at both ends (1-letter/digit names are OK).
	// Aka /[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?/.
	if len(s) < 1 || !isLetterDigit(s[0]) {
		return 0, false
	}
	i := 1

		return &ModuleError{Path: path, Err: err}
	}
	return nil
}

// firstPathOK reports whether r can appear in the first element of a module path.
// The first element of the path must be an LDH domain name, at least for now.
// To avoid case ambiguity, the domain name must be entirely lower case.
func firstPathOK(r rune) bool {
	return r == '-' || r == '.' ||
		'0' <= r && r <= '9' ||
		'a' <= r && r <= 'z'

		}
	}

}

func TestLookupNonLDH(t *testing.T) {
	defer dnsWaitGroup.Wait()

	if fixup := forceGoDNS(); fixup != nil {
		defer fixup()
	}

	// "LDH" stands for letters, digits, and hyphens and is the usual
	// description of standard DNS names.
	// This test is checking that other kinds of names are reported
	// as not found, not reported as invalid names.