Examples

        <%= 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.