docs: def filter_from_alias(self, alias, backend=None):
          """
          Return aliases that start with the given `alias`, optionally filtered
          by backend.
          """
          def alias_filter(key_item):
              key, item = key_item
  
              return ((alias is None or alias in key) and
                      (backend is None or item.backend == backend))
  
          items = six.moves.filter(alias_filter, six.iteritems(self))
  
          aliases = collections.OrderedDict(sorted(items, key=lambda a: a[0].lower()))
  
          return aliases