code: def all(self):
          
          if not self.is_any and not self.is_none:
              return [Element.from_href(href)
                      for href in self.get(self.typeof)]
          return []
docs: Return all destinations for this rule. Elements returned
          are of the object type for the given element for further
          introspection.
  
          Search the fields in rule::
  
              for sources in rule.sources.all():
                  print('My source: %s' % sources)
  
          :return: elements by resolved object type
          :rtype: list(Element)