FlagTag

FlagTag class is used for tags, that do not have any value. When parsed, that value is set to true.

class Foo
{
    /**
     * @required
     */
    public $value;
}

$doc = (new ReflectionFunction('foo'))->getDocComment();
$customTags = [new FlagTag('required')];

$notations = getNotations($doc, $customTags);
var_export($notations);

That results in

[
    'required' => true
]