code: public Set<ElementDescriptor<?>> getProperties()
  	{
  		return mProp == null ? null : Collections.unmodifiableSet(mProp.keySet());
  	}
docs: Returns an modifyable {@link Set} of properties that have been requested. The result may be <code>null</code> if there are no properties.
  
  @return A {@link Set} of {@link ElementDescriptor}s, one for each requested property or <code>null</code>.