Using of inMethods

[Jochen Kötter]

Hi,

I am creating a Database via API and I want to create a field 'Age'  
which is calculated from the field 'Birthday'.
In the Example-db  for 'inMethod' I only find UPPER() or  2*4  and  
the Doku only speakes about 'Literals'.
I tried to use Datediff and curdate() or current_date. Furthermorey I  
found nothing about Syntax for using a FieldRef in an inMethod.
I want to concieve the potential of inMethod.

Could anyone tell me a link, where the possibilities of using  
inMethods are described, please?
Could anyone give me examples about using the inMethod, please?

Greetings
Jochen Kötter