# Java Client Customizing

## Handling of Combined Forms

| The JET layer has a list of supported userexits that open tabs (i.e. bvb_usx_cmb_rpl and iwf_cyc_lis). If one of them is detected, the submasks are only opened once and remain open as long as the combined form is open, too. So the pre-mask triggers for such submasks are usually fired only once. If however the userexit is unknown, it is executed and the widget opened by this userexit is displayed in the tab. This mechanism is used for instance in the LogiView form. All fields of subforms - i.e. tabs using the F> - need to be added to the main form as invisible fields. The best way of adding the invisible fields is to add the whole submask as a mask component to the main form. Please look at a standard mask like EDB-PRO-CFR to see how this can be done. Combined forms that are still using the old mechanism to support more than one subform (with the /i=... and /v=... arguments to bvb_usx_cmb_rpl) must be adapted to the F> mechanism, which is supported by iwf_cyc_lis and bvb_usx_cmb_rpl.