10up is very well regarded WordPress development firm that does a great job of giving back to the WordPress community. 10up has a living Engineering Best Practices document that is a great resource for advanced developers:
From the 10up Engineering Best Practices page:
The 10up Engineering Best Practices are not geared to teach anyone to become an engineer. Rather, they aim to illustrate how to engineer the 10up way. Therefore, these best practices are intended for capable engineers.
In this WordPress Engineering Best Practices document they cover Markup, CSS, PHP, JavaScript, Tools, and Project structure. Thankfully, for the community they have the skill and engineering know-how to maintain a public document like this. You can even contribute at the project’s 10up Engineering Best Practices Github Repository.
