I've been dabbling with #eleventy for a couple days now and I start to understand what the fuzz is about.
#ShortCodes are a very handy feature!
I created this one cause I want to escape HTML tags properly when writing about them:
eleventyConfig.addShortcode("code", (content) => `<code><${content}></code>`,);
Which can be used like this: {% code "aside" %}