Comment by dspillett

> > Yes, you must copy and paste content and not having layout page is annoying at time

> I think this was one of the most common usages of PHP in the beginning,

> <?php include('header.inc'); ?>

And other tools beforehand: basic CGI or even more basic server-side includes (https://en.wikipedia.org/wiki/Server_Side_Includes)

To reduce CPU and IO load on the server (or just in circumstances where SSI was not enabled on the server they had available) some would pre-process the SSI directives (obviously this doesn't work for dynamic results such as the output from many #exec examples), so all that is being served is simple static files ‑ a precursor to more complex modern static site builders.

> It would be great if HTML had a similar capability. People have asked for it for over 30 years, so it's unlikely that it will be implemented now.

That doesn't really fit with the intentions of HTML, and could impose a bunch of extra network latency overhead compared to using SSI instead, leading to either complete rendering delays or jumpy pages as included content is merged in in steps, though I have seen it implemented multiple ways using a bit of JS (some significantly more janky than others).