code: private LinkedHashMap<PrefixedName,DTDElement> getElementMap() {
          LinkedHashMap<PrefixedName,DTDElement> m = mElements;
          if (m == null) {
              /* Let's try to get insert-ordered Map, to be able to
               * report redefinition problems in proper order when validating
               * subset compatibility
               */
              mElements = m = new LinkedHashMap<PrefixedName,DTDElement>();
          }
          return m;
      }
docs: /*
  /////////////////////////////////////////////////////////
  Data struct access
  /////////////////////////////////////////////////////////