Navigator 2.0, Internet Explorer 3.0; extended to be writable in Navigator 3.0
The selectedIndex property of the Select object is an integer that specifies the index of the selected option within the Select object. If no option is selected, selectedIndex is -1. If more than one option is selected, selectedIndex specifies the index of the first one only.
In Navigator 2.0, selectedIndex is a read-only property. In Navigator 3.0, it is read/write: by setting the value of this property, you cause the specified option to become selected. You also cause all other options to become deselected, even if the Select object has the MULTIPLE attribute specified. When doing list-box style selection (instead of drop-down menu selection) you can deselect all options by setting selectedIndex to -1. Note that changing the selection in this way does not trigger the onchange() event handler.
When the MULTIPLE attribute is specified and selection of multiple options is allowed, the selectedIndex property is not very useful. In this case, to determine which options are selected, you should loop through the options array of the Select object, and check the selected property of each Option object.