PHPCodeSniffer helps us stick to same coding standards across MediaWiki and its extensions.
In MediaWiki core and various MW extensions, we have PHP CS rules in a file called .phpcs.xml that are excluded because the code repository has various violations. In most cases, these can't be fixed automatically.
Remove a sniff from the .phpcs.xml file, run composer phpcs or phpcs -p -s, get a list of violations, provide patches in Wikimedia Gerrit to fix the violations. If you fix all violations for one sniff, also commit the removal of the exclusion from .phpcs.xml too.
Fix some (define a number here?) of these up.