code: private static boolean isVariableName( StringBuilder builder ) {
          for( int i = 1; i < builder.length(); ) {
              char ch = builder.charAt( i++ );
              switch( ch ) {
                  case '(':
                  case '\"':
                      return false;
              }
          }
          return true;
      }
docs: If the builder contains a valid variable name
  @param builder the builder
  @return true, if a variable; false, if it is an at-rule.