code: private double getPercent( int idx, double defaultValue, CssFormatter formatter ) {
          if( parameters.size() <= idx ) {
              return defaultValue;
          }
          return ColorUtils.getPercent( get( idx ), formatter );
      }
docs: Get the idx parameter from the parameter list as percent (range 0 - 1).
  
  @param idx
  the index starting with 0
  @param defaultValue
  the result if such a parameter idx does not exists.
  @param formatter
  current formatter
  @return the the percent value