code: public void onQueryFilterChange(final String currentText, final boolean valid, final String validationMessage) {
          if (valid) {
              showValidationSuccesIcon(currentText);
          } else {
              showValidationFailureIcon(validationMessage);
          }
          listeners.forEach(listener -> listener.queryChanged(valid, currentText));
      }
docs: Called when the filter-query has been changed in the textfield, e.g. from
  client-side.
  
  @param currentText
  the current text of the textfield which has been changed
  @param valid
  {@code boolean} if the current text is RSQL syntax valid
  otherwise {@code false}
  @param validationMessage
  a message shown in case of syntax errors as tooltip