I feel like we went a bit off on a tangent there with iframes, DOM elements and whatnot...
The main issue I see here is the lack of a simple way of layouting various elements. A better way of controlling their placement. (As Fengist also pointed out)
I made this pen as an example, it´s basically a Legend of Zelda health bar. (Give or take 5 minutes of work)
So what does it do: All of the hearts are neatly aligned, you can add/remove hearts and it has multiple rows. Also you can move the container anywhere, the hearts follow automatically.
How about Construct in this case?
Ok so we want the hearts to move with a container, so I used a tiled background as reference point. It´s basically the flexbox. But here is the first thing: It (kind of) requires a setup function at runtime, that is not the biggest issue though!
The main thing is to have the hearts neatly aligned and wrap automatically. It will require some mental gymnastics...
Look at it... none of that was required in the pen I made, because flexbox does all that shizzle for me. To be fair, it didn´t take much longer than writing the pen for me, but one should consider that this is not only a really really simple case, but also I had to deal with this exact issue beforehand and I have a couple years of experience on my back. A newbie probably will sit there without any clue where to even begin, and that´s just the tip of the iceberg.
I mean... if you have an easier way of doing it, please tell me! (And no, I wouldn´t consider using arrays easier or reasonable for such a case)
Almost forgot to mention. This is pretty hardcoded now and I´d have to go into the code to change how many hearts are shown per row etc. For flexbox, nothing required, just change the width of the container and you´re done. Especially fun if you intend to do such a thing at runtime :^)