yii\web\HeaderCollection::has PHP 메소드

Returns a value indicating whether the named header exists.

public has ( string $name ) : boolean
$name	string	the name of the header
리턴	boolean	whether the named header exists

    public function has($name)
    {
        $name = strtolower($name);
        return isset($this->_headers[$name]);
    }

HeaderCollection