yii\grid\DataColumn::renderHeaderCellContent PHP Method

    protected function renderHeaderCellContent()
    {
        if ($this->header !== null || $this->label === null && $this->attribute === null) {
            return parent::renderHeaderCellContent();
        }
        $label = $this->getHeaderCellLabel();
        if ($this->encodeLabel) {
            $label = Html::encode($label);
        }
        if ($this->attribute !== null && $this->enableSorting && ($sort = $this->grid->dataProvider->getSort()) !== false && $sort->hasAttribute($this->attribute)) {
            return $sort->link($this->attribute, array_merge($this->sortLinkOptions, ['label' => $label]));
        } else {
            return $label;
        }
    }

 public function renderHeaderCellContent()
 {
     if ($this->header !== null || $this->label === null && $this->attribute === null) {
         return parent::renderHeaderCellContent();
     }
     $provider = $this->grid->dataProvider;
     if ($this->label === null) {
         if ($provider instanceof ActiveDataProvider && $provider->query instanceof ActiveQueryInterface) {
             /* @var $model Model */
             $model = new $provider->query->modelClass();
             $label = $model->getAttributeLabel($this->attribute);
         } else {
             $models = $provider->getModels();
             if (($model = reset($models)) instanceof Model) {
                 /* @var $model Model */
                 $label = $model->getAttributeLabel($this->attribute);
             } else {
                 $label = Inflector::camel2words($this->attribute);
             }
         }
     } else {
         $label = $this->label;
     }
     return $this->encodeLabel ? Html::encode($label) : $label;
 }