This project start because of a challenge a joomler friend of mine posted in JUG Breizh on FB on February 16th 2021 The challenge was:
Given an url structure like:
/parent-category/subcat-a/article-1 /parent-category/subcat-a/article-2 /parent-category/subcat-c/article-7
How to make it work with urls like:
/parent-category/article-1 /parent-category/article-2 /parent-category/article-7
In other words without the subcategory
The answer to that delicious puzzle was custom router rules.
TLDR; Custom router rules injected via a system plugin onAfterInitialise event just right after Joomla! started "booting"