Syntax
<input onBlur="....">

This is an event which causes a script (e.g. JavaScript) to execute when an element loses focus either by the pointing device or by tabbing navigation. It may be used with the same elements as onfocus.

An example of this would be:
<input onBlur='javascript:alert("The input box has lost focus (BLURred)");' value="eluk - the best CSS help file in the world!!!!"> <b>Now click on the "comment" button below</b>

Now click on the "comment" button below