tis 2019-05-14 klockan 15:41 -0400 skrev Stefan Monnier:

> Yes, please.  I'd recommend a `regexp-` prefix for it.

Well, since you asked so nicely!

> [ And I'll carefully avoid having an opinion on the rest of the name.
> ]

The correct name is obviously something like `regexp-empty', but I have
to concede that it might be misinterpreted. The attached patch uses
`regexp-unmatchable' which is reasonably descriptive. Better
suggestions are welcome.