Ngôn ngữ HTML - Nhóm tùy chọn bên trong thẻ select

Nhóm tùy chọn bên trong thẻ select

<!DOCTYPE html>
<html lang="en">
<head>
    <title>Example of HTML optgroup tag</title>
</head>
<body>
    <form>
        <select>
            <optgroup label="Sports cars">
                <option value="ferrari">Ferrari</option>
                <option value="lamborghini">Lamborghini</option>
            </optgroup>
            <optgroup label="Luxury cars">
                <option value="mercedes">Mercedes</option>
                <option value="bentley">Bentley</option>
            </optgroup>
        </select>
    </form>
</body>
</html> 

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