parameters: (cls, type, reduce)
docstring: Register a reduce function for a type.
docstring_summary: Register a reduce function for a type.
docstring_tokens: Register a reduce function for a type .
function: def register(cls, type, reduce):
          '''Register a reduce function for a type.'''
          cls._extra_reducers[type] = reduce
function_tokens: def register ( cls , type , reduce ) : cls . _extra_reducers [ type ] = reduce