code: public void setCaseLevelDefault() {
          checkNotFrozen();
          CollationSettings defaultSettings = getDefaultSettings();
          if(settings.readOnly() == defaultSettings) { return; }
          CollationSettings ownedSettings = getOwnedSettings();
          ownedSettings.setFlagDefault(CollationSettings.CASE_LEVEL, defaultSettings.options);
          setFastLatinOptions(ownedSettings);
      }
docs: Sets the case level mode to the initial mode set during construction of the RuleBasedCollator. See
  setCaseLevel(boolean) for more details.
  
  @see #setCaseLevel(boolean)
  @see #isCaseLevel