anchor.diff:          : new XmlName(name, _lookup(uri));
     }
   
  -  // Internal method to lookup an uri prefix.
  +  // Internal method to lookup an namespace prefix.
     String _lookup(String uri) {
       var builder = _stack.lastWhere(
         (builder) => builder.namespaces.containsKey(uri),
  
positive.code:   /**
     * Binds a namespace `prefix` to the provided `uri`. The `prefix` can be
     * omitted to declare a default namespace. Throws an [ArgumentError] if
     * the `prefix` conflicts with an existing delcaration.
     */
    void namespace(String uri, [String prefix]) {
      if (prefix == _XMLNS || prefix == _XML) {
  
negative.code:  *
   * API is not finalized yet, do not use.
   */
  class XmlBuilder {
  
    final List<_XmlNodeBuilder> _stack = new List.from([new _XmlDocumentBuilder()]);
  
  