10. Scrolling menus

You can also provide a menu that shows the choices as a scrollable list:

<select name="fieldName" size="nVisible" multiple>
  <option selected>first option
  <option>second option
  …
</select>

where:

fieldName: is an internal name that will be passed to the downstream CGI script as the name of this element.
nVisible: is a number that specifies how many choices will be visible at one time. For example, size=8 would specify a scrolling list with room for eight entries at once.
multiple: is an optional attribute; if specified, it allows more than one choice to be selected at a time.

If you use the multiple attribute, you can have more than one <option selected> choice in the list of options.

HTML 4.0 fill-out forms