docs: protected final void addUserTag(String name, URL source)
      {
          if (_strictJsf2FaceletsCompatibility == null)
          {
              MyfacesConfig config = MyfacesConfig.getCurrentInstance(
                      FacesContext.getCurrentInstance().getExternalContext());
  
              _strictJsf2FaceletsCompatibility = config.isStrictJsf2FaceletsCompatibility();
          }
          if (Boolean.TRUE.equals(_strictJsf2FaceletsCompatibility))
          {
              _factories.put(name, new LegacyUserTagFactory(source));
          }
          else
          {
              _factories.put(name, new UserTagFactory(source));
          }
      }