Interaction between Application Forms and Collections 

If a collection calls up an application form, information about the context is transferred to the application form, together with data and selection information. The application form receives the information about the name of the calling collection via the variable C-COLLECTION and the identification via the variable C-IDENTIFICATION.
You can also deliver additional information to the application form via the variable C-T_GENDATA. This could originate from other application forms processed in a previous step or, for example, from a user exit in the calling collection. An application form can also return data by creating lines of the type EFG_STR_GENDATA in a user exit for processing later in another application form. You have to insert these lines in the global export parameter Y_TAB_GENDATA or the global field symbol <Y_TAB_GENDATA>.
In cross-form class collections, you can also control the selection options transferred for the application forms called via the parameter C-T_SEL_PER_FCLASS. If the line for the respective form class was not transferred by the calling application, you have to add it to this table. This is the only way the form class can recognize it.