Using ABAP programming, you can enhance the function and dynamics of an application form as required. The ABAP implementations required are stored in customer-defined includes in the USER-EXIT-INCLUDE and the USER-TOP-INCLUDE. The names of both ABAP includes are defined in the attributes of an application form.
Data instructions (for example, DATA: TOTAL TYPE <Data type>) are implemented in the USER-TOP-INCLUDE, the user exit subroutines are defined in the USER-EXIT-INCLUDE.
Since user includes are client-independent as ABAP program objects, under certain circumstances, different application forms can reference to the same user include from different clients. Note therefore, that a user include or referenced application forms can be changed or invalidated by unintentional changes as part of maintenance of other application forms.
The user includes are included in the TOP included in the generated function groups of an application form. The user exits defined in the user exit include are called in the defined events for the form levels (for example, before, during, after loop). You can also define and call other user-defined form routines.