Yii 1 Pjax

Backport of Yii 2's Pjax widget for Yii 1

Works the same as in Yii 2:

use pinfirestudios\\yii1pjax\\Pjax;
...
$this->beginWidget(Pjax::class);
    ...
$this->endWiget();

This has only been tested for our specific use case, so there may be bugs.