That's kind of right, but they are adding new literals, not changing existing ones. The hooks are for the lexer and they can decide what syntax they accept. The syntax it defines would be a parse error if the hook is not used. But, indeed, this can be misused by accepting too much though, for instance when an IP addr also accepts a float. So the hook needs to be a bit careful.

The `#cidr{...}` syntax would work but then it wouldn't be much more convenient than just constructing the value with normal functions, I think.