Adding Form Input Controls - Stripes...and Java Web Development is Fun Again - page 161

Figure 8.3: The Message Compose page
Using Multiple Selection Boxes
Select boxes can also allow the user to select more than one item at a
time. For example, the Message Compose page, shown in Figure 8.3 ,
has a select box on the right side that contains the list of contacts. The
user can easily add recipients by selecting the contacts and clicking
one of the arrow buttons.
To allow multiple selection in the select box, add multiple= "true" to the
<s:select> tag and, optionally, the size= attribute to indicate how many
rows to show at a time.