code: public static MetaClassRegistry getInstance(int includeExtension) {
          if (includeExtension != DONT_LOAD_DEFAULT) {
              if (instanceInclude == null) {
                  instanceInclude = new MetaClassRegistryImpl();
              }
              return instanceInclude;
          } else {
              if (instanceExclude == null) {
                  instanceExclude = new MetaClassRegistryImpl(DONT_LOAD_DEFAULT);
              }
              return instanceExclude;
          }
      }
docs: Singleton of MetaClassRegistry.
  
  @param includeExtension
  @return the registry