Does anyone know of an easy way to create a sub-menu (check box's, multiple select, or radio button)? Following is some example code I've used, I have the multiple select feature working however, I'd like to select one item from the menu and have it take me to a related sub-menu to select from again.

return "<select name=ERROR_CODE[] size=4 multiple>
<optgroup label=ExcessFlyTime>
<OPTION>EXF
<OPTION>XYZ
</optgroup>
<optgroup label=MissingActuals>
<OPTION>MSA
<OPTION>AAA
</optgroup>
<optgroup label=OutOfOrderDepArr>
<OPTION>OOD
<OPTION>BBB
<OPTION>CCC
</optgroup>
<optgroup label=OutOfSyncItinNum>
<OPTION>OSI
<OPTION>DDD
<OPTION>EEE
<OPTION>FFF
<OPTION>GGG
</optgroup>
</SELECT>";