code: public List<UrlCss3Value> getUrlCss3Values() {
          // for security improvements for urlCss3Values without
          // compromising performance.
          // TODO the drawback of this the returning of new object each time even
          // if the urlCss3Values array has not been modified, as a minor
          // performance
          // improvement, return a new object only if the urlCss3Values is
          // modified.
          if (urlCss3Values == null) {
              return null;
          }
          return Collections.unmodifiableList(Arrays.asList(urlCss3Values));
      }
docs: @return a new object of unmodifiable {@code List<UrlCss3Value>} whenever
  this method is called. Or null.
  
  @author WFF
  @since 1.0.0