code: def is_url_for(cls, _action, _endpoint=None, _app=None, _external=None, **paramattrs):
          
          def decorator(f):
              if 'url_for_endpoints' not in cls.__dict__:
                  cls.url_for_endpoints = {None: {}}  # Stick it into the class with the first endpoint
              cls.url_for_endpoints.setdefault(_app, {})
  
              for keyword in paramattrs:
                  if isinstance(paramattrs[keyword], six.string_types) and '.' in paramattrs[keyword]:
                      paramattrs[keyword] = tuple(paramattrs[keyword].split('.'))
              cls.url_for_endpoints[_app][_action] = _endpoint or f.__name__, paramattrs, _external
              return f
          return decorator
docs: View decorator that registers the view as a :meth:`url_for` target.