docs: def getDefaultShareID(store):
      """
      Get the highest-priority default share ID for C{store}.
  
      @return: the default share ID, or u'' if one has not been set.
      @rtype: C{unicode}
      """
      defaultShareID = store.findFirst(
          _DefaultShareID, sort=_DefaultShareID.priority.desc)
      if defaultShareID is None:
          return u''
      return defaultShareID.shareID