I wrote:
> We can't allow '-', for the specific reason that it won't work as a -c
> argument (thanks to -c's translation of '-' to '_'). The whole point here
> is to prevent corner cases like that. ':' would be all right, but I think
> it's a lot simpler to explain and a lot harder to break in future if we
> just say that the names have to be valid identifiers.
Hearing no further comments, I pushed the more restrictive version.
regards, tom lane