When specifying the properties of a form what is the difference between:

Code:
<FORM action="rar.asp" onSubmit="function()">
  <INPUT type="hidden" value="foo">
</FORM>

and 

<FORM action="rar.asp" onSubmit="return function()">
  <INPUT type="hidden" value="foo">
</FORM>
(onSubmit bit....)

Cheers!