code: protected void addAccessor(PathAccessor acc, Class<? extends BioPAXElement> clazz)
  	{
  		accessors.put(acc, clazz);
  	}
docs: Adds the given <code>PathAccessor</code> to the list of accessors to use to get field values
  of objects and their related objects.
  @param acc accessor
  @param clazz the type of element that the accessor is applied