I 100% agree with the sentiment of this article. For my personal website, I write pretty much every page by hand, and I have a header and a footer on most of those pages. I certainly don't want to have to update every single page everytime I want to add a new navigation button to the top of the page. For a while I used PHP, but I was running a PHP server literally for only this feature. I eventually switched to JavaScript, but likewise, on a majority of my pages, this was the only JavaScript I had, and I wanted to have a "pure" HTML page for a multitude of reasons.

In the end, I settled on using a Caddy directive to do it. It still feels like a tacked on solution, but this is about as pure as I can get to just automatically "pasting" in the code, as described in the article.