This is a feature that was introduced in version 2.17 and is described here in the release notes:
https://webwork.maa.org/wiki/Release_notes_for_WeBWorK_2.17
The current version of WeBWorK is 2.19. If you plan to upgrade WeBWorK to 2.19, I would recommend doing a fresh installation rather than literally upgrading. You could migrate courses to the new installation using course archives.
The jump from 2.16 to 2.17 is not as severe as the one from 2.17 to 2.18, and you may be able to upgrade to 2.17 in place without too much difficulty. But I can't recommend one way or the other about trying this.