code: public static <D extends BioPAXElement, R> PropertyAccessor<D,R> create(PropertyAccessor<D,R> pa,
  	                                                                                     Class filter)
  	{
  		 return new FilteredPropertyAccessor<D, R>(pa, filter);
  	}
docs: FactoryMethod that creates a filtered property accessor by decorating a given accessor with a class filter.
  @param pa to be decorated
  @param filter Class to be filtered, must extend from R.
  @param <D> Domain of the original accessor
  @param <R> Range of the original accessor
  @return A filtered accessor.