Custom Validation on a Field

Hello there
 
Is it possible to use a Javascript function to validate a field, rather than use the “Validation Pattern” approach? I am Ok to write the function, however I also want to be able to use it with the Form Level Validation Settings (having the function run again when the form submits etc.).
 
I have seen references to the “Run custom validation script” option on a Validate tab, however I don’t see these.
 
I am using LiveCycle Designer 9.
 
Many thanks
 
Geoff Olding