code: function(){
                  /*            
                   * negation
                   *   : NOT S* negation_arg S* ')'
                   *   ;
                   */
  
                  var tokenStream = this._tokenStream,
                      line,
                      col,
                      value       = "",
                      arg,
                      subpart     = null;
                      
                  if (tokenStream.match(Tokens.NOT)){
                      value = tokenStream.token().value;
                      line = tokenStream.token().startLine;
                      col = tokenStream.token().startCol;
                      value += this._readWhitespace();
                      arg = this._negation_arg();
                      value += arg;
                      value += this._readWhitespace();
                      tokenStream.match(Tokens.RPAREN);
                      value += tokenStream.token().value;
                      
                      subpart = new SelectorSubPart(value, "not", line, col);
                      subpart.args.push(arg);
                  }
                  
                  return subpart;
              }
docs: CSS3 Selectors