[WebIDL] cycles in [PutForward] chains

In [1], the following language appears:

Note that [PutForwards] <http://www.w3.org/TR/WebIDL/#PutForwards>
> -annotated attributes <http://www.w3.org/TR/WebIDL/#dfn-attribute> can be
> chained. That is, an attribute with the [PutForwards]<http://www.w3.org/TR/WebIDL/#PutForwards>
>  extended attribute <http://www.w3.org/TR/WebIDL/#dfn-extended-attribute> can
> refer to an attribute that itself has that extended attribute. Theremust
> not exist a cycle in a chain of forwarded assignments. A cycle exists if,
> when following the chain of forwarded assignments, a particular attribute
> on an interface <http://www.w3.org/TR/WebIDL/#dfn-interface> is
> encountered more than once.


While this states that a cycle must not exist, it fails to define
implementation behavior regarding cycle detection and action in the
presence of a cycle. If this is intentionally left undefined, perhaps that
should be stated.

[1] http://www.w3.org/TR/WebIDL/#PutForwards