What I found while reviewing https://github.com/phetsims/joist/issues/873 (mostly unrelated, but had changes to ScreenView voicing code) was that responseCollector could collect a response that was a function, and it would pass that function directly to stringUtils.fillIn
Types are passing now, and things should much less sloppy. Just because nothing was currently passing it in doesn't mean that couldn't happen in the future.
What I found while reviewing https://github.com/phetsims/joist/issues/873 (mostly unrelated, but had changes to ScreenView voicing code) was that responseCollector could collect a response that was a function, and it would pass that function directly to stringUtils.fillIn
https://github.com/phetsims/utterance-queue/blob/6a48435a915bd55435dd94cdb7fb2c9853e873e6/js/responseCollector.ts#L91-L96
We can tighten that up to just be a fillable value or a Property.