Tilda (~) and (+) at the end of add-on version?

‘Customize Keyboard Shortcuts’ add-on.
On website, the version 2.1.21~ is shown; but inside the Description it is 2.1.21+. Please explain.

Will the add-on work on Anki 2.1.22 ?
Should i wait for the add-on update at the next update cycle?
Thank you all for sharing your add-ons.

It means the add-on author tested on .21. It may work on newer versions as well.