How to use OnBlur in CRM Web UI

Hi,

I would like to use the JavaScript event 'OnBlur' in a field in CRM Web UI so that I can trigger a server roundtrip after the user left the focus of a field. How can this be done (using CRM 7.0 EhP1).

I found a couple of articles but those were more in the area of Web Channel, Portal, etc...

Thanks,

Sebastian