onChange
The instruction(s) to be executed are placed within quotes. This event handler will execute the instruction(s) when a change has been made to the object to which it has been assigned. A change can be the typing of new characters, or even a change of focus from the default focus point.

The following example will display text of your choice within a message box when the 'onChange' event handler is activated:
onChange="msgWindow.document.write('-- Insert desired text message here --')"
This Event Handler is used with the following:

BODY
CAPTION
DIV
FIELDSET
IMG
LEGEND
SELECT
TEXTAREA