<iframe>
A nested browsing context — another document embedded in this one.
Baseline: Widely available · Media & embedded content
When to use it
For embeds you can't inline (maps, videos, sandboxed widgets); always with title for assistive tech and loading='lazy' below the fold.
When not to
Every iframe costs a document fetch and layout — use sparingly, and sandbox untrusted content.
Key attributes
src / srcdoc- the embedded document
title- accessible name (required in practice)
loading- lazy
sandbox / allow- capability restrictions
width / height
Example
<iframe title='A minimal embedded document' srcdoc='<p>Hello from inside.</p>' width='320' height='80' loading='lazy'></iframe>