If I want the user to select one or more items the HTML symantecally correct form element would be
<select multiple id="sel"> <option>Option 1</option> <option>Option 2</option> <option>Option 3</option> <option>Option 4</option> <option>Option 5</option> </select>
Which looks like this:.
The user can choose multiple elements by Ctrl or Shift clicking items.
This is the standard widget used by browsers, but is this the best way to display this kind of input? Do users understand it?