yii\web\HeaderCollection::getIterator PHP Метод

This method is required by the SPL interface [[\IteratorAggregate]]. It will be implicitly called when you use foreach to traverse the collection.

public getIterator ( ) : ArrayIterator
Результат	ArrayIterator	an iterator for traversing the headers in the collection.

    public function getIterator()
    {
        return new ArrayIterator($this->_headers);
    }

HeaderCollection