parameters: (self, boxes, anchors)
docstring: Method to be overridden by implementations.
  
          Args:
            boxes: BoxList holding N boxes to be encoded
            anchors: BoxList of N anchors
  
          Returns:
            a tensor representing N relative-encoded boxes
docstring_summary: Method to be overridden by implementations.
docstring_tokens: Method to be overridden by implementations .
function: def _encode(self, boxes, anchors):
          """Method to be overridden by implementations.
  
          Args:
            boxes: BoxList holding N boxes to be encoded
            anchors: BoxList of N anchors
  
          Returns:
            a tensor representing N relative-encoded boxes
          """
          pass
function_tokens: def _encode ( self , boxes , anchors ) : pass