Hello again. Thank you very much @sbassett for the explanation. I would love to complete this task, however someone with deeper knowledge of the extension submodule structure may be better equipped to complete this. Thanks again to everyone that assisted and commented.

Hey Gergő. Hope you are doing well. I wanted to check back in on this to ensure that CheckMatrixWidget.php needs updating. I will update the test later today.

Thanks for taking a look. Looking at CheckMatrixWidget.php , it looks to be using OOUI ? If that isn't the case I can add to my feature branch. Which extensions should be updated? I am happy to take that on if it is in scope for this ticket.

Thanks Gergő. Understood; I would agree with that. After tracing through each result from the regex you provided (thanks), I am only seeing two direct uses of HTMLForm:

Gergő - I really appreciate the detailed response and advice. With that information, I'm going to give it another shot.

I added a topic branch to get started on this. Before I continue I wanted to ensure I'm on the right path. I am a new contributor and have a couple of questions:

I could take this on. The way I'm searching for deprecated usage is: 'help' => wfMessage; if I'm missing something, please let me know. Cheers and happy Thanksgiving for those who celebrate.