For some time, [Drupal's PHP coding standards](https://www.drupal.org/docs/develop/standards/php/php-coding-standards#s-functions-and-variables) allows for writing variables in either snake-case (e.g. `$my_variable`) or lower camel-case (`e.g. $myVariable`).
It originally only allowed for snake-case variable names but once it accepted both, I switched to camel-case as my default.
Why? I didn't like the inconsistency of using one approach for variable names and one for method and property names in PHP classes (which were always camel-case).
I'd have had code like this with a mixture of both:
I prefer not to have to consistently think about which to use and, if possible, like to use standard approaches in different codebases whether I'm working on a Drupal project, a Symfony project, or a PHP library.
Plus, I get to use new PHP features like [promoted constructor properties](https://www.oliverdavies.uk/archive/2023/04/12/cleaner-php-code-with-promoted-constructor-properties) if everything is named in the same format.