docs: function findFormatFunction(that, method, format) {
          var ff, defFormat;
          if (format) ff = that.getFormat(format);
          if (ff) {
              if (!ff[method]) {
                  that.throwErr('Error', method, 'format ' + format + ' found, ' +
                                'but method ' + method + ' not available');
              }
              ff = ff[method];
          }
          // Try to get default format, if the extension is not recognized.
          if (!ff) {
              defFormat = that.getDefaultFormat();
              if (!defFormat) {
                  that.throwErr('Error', method, 'format ' + format + ' not ' +
                                'found and no default format specified');
              }
              ff = that.getFormat(defFormat, method);
              if (!ff) {
                  that.throwErr('Error', method, 'format ' + format + ' not ' +
                                'found, but default format has no method ' +
                                method);
              }
          }
          return ff;
      }