Documentation page on render arrays.
Enable twig debugging in your site's services.yml or development.services.yml. parameters: twig.config: debug: true
You can "autowire" your services, or automatically define their dependencies in *.services.yml based on their class...
If you are overriding a library that is already overridden by a base theme, use the base theme's full path to the file...
Documentation for XHProf module.