framework/widgets/FragmentCache.php
public function init()
    {
        parent::init();

        $this->cache = $this->enabled ? Instance::ensure($this->cache, 'yii\caching\CacheInterface') : null;

        if ($this->cache instanceof CacheInterface && $this->getCachedContent() === false) {
            $this->getView()->pushDynamicContent($this);
            ob_start();
            ob_implicit_flush(false);
        }
    }
public function init()
    {
        parent::init();

        $this->cache = $this->enabled ? Instance::ensure($this->cache, 'yii\caching\CacheInterface') : null;

        if ($this->cache instanceof CacheInterface && $this->getCachedContent() === false) {
            $this->getView()->pushDynamicContent($this);
            ob_start();
            ob_implicit_flush(false);
        }
    }
Initializes the FragmentCache object.