The code follows the Drupal coding standards:
https://www.drupal.org/coding-standards

Style compliance can be checked using the Coder Sniffer extension to the PEAR
PHP_CodeSniffer project, for instructions about how to install Coder Sniffer
see https://www.drupal.org/node/1419988

TL;DR: install drupla/coder and enable the Drupal coding standard in
PHP_CodeSniffer:
  
  $ composer global require drupal/coder
  $ export PATH="$HOME/.config/composer/vendor/bin:$PATH"
  $ phpcs --config-set installed_paths $HOME/.config/composer/vendor/drupal/coder/coder_sniffer/

And then use this command to check the style:

  $ phpcs --standard=Drupal .
