code: protected void registerAttributes(XAttributeInfoImpl attributeInfo, XAttributable attributable) {
  		if (attributable.hasAttributes()) {
  			for(XAttribute attribute : attributable.getAttributes().values()) {
  				// register attribute in appropriate map
  				attributeInfo.register(attribute);
  				// register meta-attributes globally
  				registerAttributes(metaAttributeInfo, attribute);
  			}			
  		}
  	}
docs: Registers all attributes of a given attributable, i.e.
  model type hierarchy element, in the given attribute info registry.
  
  @param attributeInfo Attribute info registry to use for registration.
  @param attributable Attributable whose attributes to register.