should this be in the main section?

It's a good question. I decided to mirror the placement of the pre-existing page_header.html above it since it's only a single page for now. https://github.com/tc39/tc39.github.io/blob/master/_layouts/default.html#L20

For a multi-page site, I would go w/ more of a so-called “global footer” that would exist outside of the <main> element, which would have started at default.html#L27 instead.

I don't think that, because it is a single page, that the footer should be inside the main content. The purpose of the structure of <nav></nav><main></main><footer></footer> isn't for single pages vs multi-page sites -- its for semantic html. This is used by accessibility technologies and also helps keep the site well organized -- regardless of if it is a multi page site or a single page site

You can read more about that here https://developer.mozilla.org/en-US/docs/Learn/Accessibility/HTML and here https://webflow.com/blog/html5-semantic-elements-and-webflow-the-essential-guide

Let's move the footer out of the main body and, if you like -- in a separate patch deal with the nav. Looking at the code -- the nav is unnecessarily nested. There is likely cleanup there. There will probably be issues in the styling due to this nesting. That might be a nice next bug.

It's hard to read because it isn't indented, but the page header is currently nested within the <main> element.

I'm aware that the header, which contains the nav, is currently in the main section.

If you read my comment again, I proposed moving the nav in the next patch. It is nested inside of the header in a single element, which in turn is in the main section.

if you like -- in a separate patch deal with the nav. Looking at the code -- the nav is unnecessarily nested

Please move the footer out of the main section. There is no reason for it to be there.

[…] in a separate patch deal with the nav.

Do you think it would alright if this was taken care of in 0504624?

sgtm