Eg. It says ‘what is your date of birth?’ And then on the next page it says. ‘You are X years old. Is that correct?’

At the end, just before submission it showed the completed sections, and you could look at each section to see a tidy summary of the answers provided. Except for the section 1, where doing that jumped to the last of the section's questions instead.

I wanted to see one of the answers I had given in the section 1 to check before committing, and due to the missing summary page, tried stepping backwards and forwards through each question. All were shown, except the question I wanted to check (and had answered) was skipped.

Inspired to try things, I added a non-existent person to the household, then removed the non-existent person.

After that, when I stepped through all questions in section 1 it included the question and answer I'd been looking for, allowing me to confirm it was correct before submission.

Edit: Just remembered it's all open source too! Look here and search for repos beginning "eq-". Survey runner is the app I believe. When I was there the plan was to use that, though perhaps they eventually wrote a fresh app. Anyway the code should all be there https://github.com/ONSdigital?q=Eq&type=&language=&sort=

Looks like the core site is Rails but it seems they use a bit of everything. Preact, Go, Node, etc