Namespaces

Namespacing was progressively introduced for Joomla classes over a number of Joomla 3.x releases. In Joomla 4 nearly all of the Joomla classes were namespaced, and it was expected that Joomla extensions were namespaced as well.

If you're not familiar with PHP namespacing then you can find general information online, for example at https://www.php.net/manual/en/language.namespaces.php

This Joomla documentation focuses on how namespacing is implemented within Joomla. You may find this video on namespacing useful as well.