I don't think it's unusual in our code base (it's all over the place), or in PHP in general. The manual is a little misleading as it only demonstrates single line arrays, not multi-line arrays. It is quite common for trailing commas to be encouraged in multi-line arrays, see for example the [Zend Framework coding standards](http://framework.zend.com/manual/1.12/en/coding-standard.coding-style.html#coding-standard.coding-style.arrays), [Symfony's](http://symfony.com/doc/current/contributing/code/standards.html#structure), [Facebook's (as shown in Phabricator's standards)](http://www.phabricator.com/docs/phabricator/article/PHP_Coding_Standards.html), etc..