To output the text in the main window, or in the page window there are different output areas that you can select.
In the page layout, the top area always appears at the beginning of the main window. The top area can be used to automatically output headings on the subsequent pages for tables to cover multiple pages.
The output placed into the upper margin area using the print program is not formatted at once, but stored internally in SAP script initially. Formatting occurs only as soon as the print program writes text into the Body area. Variables are retrieved and replaced in that moment as well.
The Body area of the main window is filled before the program reaches the definition part of the upper margin. This definition is used as the top area for the subsequent page. You can say that it is not possible to delete a heading in the Top area after writing text into the Body area.
The Bottom margin comes at the end of the Main window. The Bottom area is defined for the current page when you complete the output of the body area. If there is not enough space left on the page, then the Bottom area text of the output is produced on the next page of the page layout.
If the print program produces the output text to the Bottom area of the Main window, it memorizes these lines for subsequent pages (just like Top lines). At the same time, the composer processes these lines to determine the space the Bottom area requires and the space left for the Body area. At this moment, it replaces the variables set in the Bottom area for the current page.