public static function button(
        string $label, 
        string $type = "submit", 
        string $onclick = null, 
        array $attributes = []
    ) : string
    {
        $buttonPreAttributes = [
            "type" => $type,
        ];
        
        if ($onclick) {
            $buttonPreAttributes["onclick"] = $onclick;
        }
        $buttonAttributes = array_merge($buttonPreAttributes, $attributes);        
        
        return self::tag("button", $label, $buttonAttributes);
    }