code: public boolean isExternal(Element element) {
          if (packageToItemMap == null) {
              return false;
          }
          PackageElement pe = configuration.utils.containingPackage(element);
          if (pe.isUnnamed()) {
              return false;
          }
          return packageToItemMap.get(configuration.utils.getPackageName(pe)) != null;
      }
docs: Determine if a element item is externally documented.
  
  @param element an Element.
  @return true if the element is externally documented