if r < utf8.RuneSelf {
		return r == '-' || r == '.' || r == '_' || r == '~' ||
			'0' <= r && r <= '9' ||
			'A' <= r && r <= 'Z' ||
			'a' <= r && r <= 'z'
	}
	return false
}

// importPathOK reports whether r can appear in a package import path element.
//
// Import paths are intermediate between module paths and file paths: we allow
// disallow characters that would be confusing or ambiguous as arguments to

	if elem == "" || elem[0] == '.' || elem[len(elem)-1] == '.' {
		return false
	}
	for i := 0; i < len(elem); i++ {
		if !importPathOK(elem[i]) {
			return false
		}
	}
	return true
}

func importPathOK(c byte) bool {
	// mask is a 128-bit bitmap with 1s for allowed bytes,
	// so that the byte c can be tested with a shift and an and.