yii\grid\DataColumn::getHeaderCellLabel PHP Method

    protected function getHeaderCellLabel()
    {
        $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);
            } elseif ($provider instanceof ArrayDataProvider && $provider->modelClass !== null) {
                /* @var $model Model */
                $model = new $provider->modelClass();
                $label = $model->getAttributeLabel($this->attribute);
            } elseif ($this->grid->filterModel !== null && $this->grid->filterModel instanceof Model) {
                $label = $this->grid->filterModel->getAttributeLabel($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 $label;
    }