if url == xmlURL {
		return xmlPrefix
	}

	// Need to define a new name space.
	if p.attrPrefix == nil {
		p.attrPrefix = make(map[string]string)
		p.attrNS = make(map[string]string)
	}

	// Pick a name. We try to use the final element of the path
	// but fall back to _.
	prefix := strings.TrimRight(url, "/")
	if i := strings.LastIndex(prefix, "/"); i >= 0 {
		prefix = prefix[i+1:]
	}