Let's make this valid:
Don't invalidate the other one, so it's backwards compatible with all those non-existent content specs out there ;-)
<Title> [N, C: <TopicID>]
where <Title> and <TopicID> must match
Added in 0.22.0.
The "C: <TopicID>" must be directly after the "N" ID (where the type would normally be for new topics).
Just for some technical details, the processor still assumes the old syntax when processing. All that was added was to convert the new syntax to the old syntax when parsing.