names. Lambda should be passed to use this option. Example:

    date_select('user_birthday', '', start_year: 1998, end_year: 2000, year_format: ->year { "Heisei #{year - 1988}" })

The HTML produced:

    <select id="user_birthday__1i" name="user_birthday[(1i)]">
    <option value="1998">Heisei 10</option>
    <option value="1999">Heisei 11</option>
    <option value="2000">Heisei 12</option>
    </select>
    /* The rest is omitted */