How do custom PHPStan or Psalm rules and extensions let a team enforce their own project specific coding standards and catch domain specific mistakes beyond the tool's built in checks?

Beyond the extensive built in checks that PHPStan and Psalm already provide, both tools support writing custom rules or extensions tailored to a specific project's own conventions and common mistakes, such as flagging direct calls to a deprecated internal helper function that should no longer be used, enforcing that a certain type of object is always constructed through a designated factory method rather than directly, or ensuring a specific naming convention is consistently followed across an entire team, letting the tool encode institutional knowledge that generic, general purpose checks alone could never capture.

final class NoDirectDatabaseQueryRule implements Rule {
    public function processNode(Node $node, Scope $scope): array {
        // custom rule logic here
    }
}