<%= dropdown
         ['Dropdown 1', id => 'a_custom_id', right, items => [
            ['Item 1', ['item1'] ],
            ['Item 2', ['item2'] ],
            [],
            ['Item 3', ['item3'] ]
         ] ] %>
    <div class="dropdown">
        <button class="btn btn-default dropdown-toggle" type="button" id="a_custom_id" data-toggle="dropdown">Dropdown 1</button>
        <ul class="dropdown-menu dropdown-menu-right">
            <li><a class="menuitem" href="item1" tabindex="-1">Item 1</a></li>
            <li><a class="menuitem" href="item2" tabindex="-1">Item 2</a></li>
            <li class="divider"></li>
            <li><a class="menuitem" href="item3" tabindex="-1">Item 3</a></li>
        </ul>
    </div>
By default, tabindex is set to -1...
    <%= dropdown
         ['Dropdown 2', caret, large, primary, items => [
            ['Item 1', ['item1'], data => { attr => 2 } ],
            ['Item 2', ['item2'], disabled, data => { attr => 4 } ],
            [],
            ['Item 3', ['item3'], data => { attr => 7 } ],
            [],
            ['Item 4', ['item4'], tabindex => 4 ],
            'This is a header',
            ['Item 5', ['item5'] ],
         ] ] %>
    <div class="dropdown">
        <button class="btn btn-lg btn-primary dropdown-toggle" type="button" data-toggle="dropdown">Dropdown 2 <span class="caret"></span></button>
        <ul class="dropdown-menu">
            <li><a class="menuitem" href="item1" tabindex="-1" data-attr="2">Item 1</a></li>
            <li class="disabled"><a class="menuitem" href="item2" tabindex="-1" data-attr="4">Item 2</a></li>
            <li class="divider"></li>
            <li><a class="menuitem" href="item3" tabindex="-1" data-attr="7">Item 3</a></li>
            <li class="divider"></li>
            <li><a class="menuitem" href="item4" tabindex="4">Item 4</a></li>
            <li class="dropdown-header">This is a header</li>
            <li><a class="menuitem" href="item5" tabindex="-1">Item 5</a></li>
        </ul>
    </div>
...but it can be overridden.