code: function(){
                  /*
                   * namespace_prefix
                   *   : [ IDENT | '*' ]? '|'
                   *   ;
                   */
                  var tokenStream = this._tokenStream,
                      value       = "";
  
                  //verify that this is a namespace prefix
                  if (tokenStream.LA(1) === Tokens.PIPE || tokenStream.LA(2) === Tokens.PIPE){
  
                      if(tokenStream.match([Tokens.IDENT, Tokens.STAR])){
                          value += tokenStream.token().value;
                      }
  
                      tokenStream.mustMatch(Tokens.PIPE);
                      value += "|";
  
                  }
  
                  return value.length ? value : null;
              }
docs: CSS3 Selectors