Making iframes be the right size is super awkward. I might actually use them more if they were easy to get responsive.

This post does link to a technique (new to me) to extract iframe contents:

    <iframe src="/example.html" onload="this.before((this.contentDocument.body||this.contentDocument).children[0]);this.remove()"></iframe>

Iframes fundamentally encapsulate html documents, not fragments.

Interaction between elements in different iframes is very restricted.