docs: def bind(cls, param=None, **kwargs):
          """Bind middleware's method as endpoint.
          """
          def stick(function, **binding):
              if not asyncio.iscoroutine(function):
                  function = asyncio.coroutine(function)
              bindings = getattr(function, STICKER, [])
              bindings.append(binding)
              setattr(function, STICKER, bindings)
              return function
          if isinstance(param, str):
              return partial(stick, prefix=param, **kwargs)
          return stick(param, **kwargs)