Field Validation config for Tranid

(OB28) IMG -> search for validation
1) Assign validation to company code
2) create validation (i.e. dat_chk)
3) create step, check, message

(GCX2) Maintain Client-Dependent User Exits activity in the Implementation Guide (IMG) for Special Purpose Ledger
1) enter the appropriate user exit program
2) maintain user exit program (ZGGBS000 and ZGGBR000 -- copied from -- RGGBS000 and RGGBR000)

Additional:
IMG -> search for Validation (OB28 for accounting docs)
IMG -> search for Substitution (OBBH for accounting docs)