The spec states: 
> Any features of Web IDL that are not in use by any Web specification
> by the time the test suite is otherwise complete will be considered
> at risk and will be dropped.
while the Process document explains: 
> In the Call for Implementations, the Working Group MAY identify
> specific features of the technical report as being "features at
> risk." General statements such as "We plan to remove any
> unimplemented feature" are not acceptable; the Working Group MUST
> precisely identify any features at risk. Thus, in response to a Call
> for Implementations, reviewers can indicate whether they would
> register a Formal Objection to the decision to remove the identified
Thanks, I wasn't aware of that restriction. I've gone back to enumerating some features that are currently or might be unused.