code: def AFF4AddChild(self, subject, child, extra_attributes=None):
      
      precondition.AssertType(child, Text)
  
      attributes = {
          DataStore.AFF4_INDEX_DIR_TEMPLATE %
          child: [DataStore.EMPTY_DATA_PLACEHOLDER]
      }
      if extra_attributes:
        attributes.update(extra_attributes)
      self.MultiSet(subject, attributes)
docs: Adds a child to the specified parent.