How to match end of input?

[gajus]

I need to distinguish between a whitespace and an empty string, i.e. foo:, foo:bar and foo: (this one has space) need to be treated differently.

Is there a special keyword for end of input?

[PoolloverNathan]

This repository seems dead, but if someone is still around, I would like to propose syntax:

• A ?= token in completeexpression which is followed by another expr. The second expr will be matched at the current position as if the ?= wasn't there, but the cursor will not be affected/will be rewinded. (It exists in my fork, but is not implemented yet.)
• A $ token at the end of completeexpression which causes it to only match at the end of input.