I thought that I had seen most everything... whoa, wrong assumption.

The request that I received includes validating a question and/or group (depending on how the admin settings are setup) at submit (or next). If the user did not answer the question(s) then they should get a javascript confirm - if the user selects cancel then it will return false back to the question(s) otherwise the submit goes through. The use case they gave is a validation message to either skip the question (confirm) or return to the question (return false).

Seems to be another usability idiot detector to me...

Has anybody else ran into this type of requirement and how did you resolve?

It's easy to interrupt the submit with a confirm message but the code that triggers it (if questions are unanswered) would depend on the question types on the page.

Is the global $notanswered boolean common to all questions and would that be a better catch/trigger?

I don't know if it's common but regardless, it's server-side which would require modifying the core code.

After a little thought it gets a little messy anyway.You would need to put in something to prevent repeat confirms if the respondent goes back and modifies/answers a question. And if it were me taking the survey, I would get real cranky after a few pages with the confirms. Most surveys are onerous enough without extra clicks.