Navigator 2.0, Internet Explorer 3.0
<INPUT TYPE="checkbox"   a definition of the handler
       onClick="handler-statements">
checkbox.onclick  a reference to the handler
checkbox.onclick();   an explicit invocation of the handler
onclick() is an event handler invoked when the user clicks on a Checkbox. This event handler is defined by the onClick attribute of the HTML <INPUT> tag that defines the Checkbox. The value of this attribute may be any number of JavaScript statements, separated by semicolons; these statements will be executed when the user clicks on (i.e., checks or unchecks) the Checkbox.