There is no theory, only the knowing.
I've been using template elements a lot recently to render products on my wife's photography blog. The product data gets loaded from a headless MedusaJS instance, plugged into a template that matches her blog's theme, and then dropped into the page. I specifically wanted to avoid reaching for something like React since the page load is already pretty heavy with the size of her images. Template's been pretty easy to use in that respect.
This project is an enhanced reader for Ycombinator Hacker News: https://news.ycombinator.com/.
The interface also allow to comment, post and interact with the original HN platform. Credentials are stored locally and are never sent to any server, you can check the source code here: https://github.com/GabrielePicco/hacker-news-rich.
For suggestions and features requests you can write me here: gabrielepicco.github.io