Mapping: ABAP call from User Function

Hi,

Some time earlier this month I remember seeing a document on how to call an ABAP function from the User defined functions in the graphical mapping editor.

Now I can't remember where I saw this, was it a forum post or a weblog or a general XI article... even though I have spent ages searching all over SDN.

Does anybody know where I can find this document?

Thanks and Regards

Manish