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• CALL FUNCTION 'OPEN_FORM'
  The function module OPEN_FORM opens form printing. You must call this function module before you can use any other form function (WRITE_FORM, START_FORM, CONTROL_FORM...).
  
  You need not specify a form name. If you omit the name, you must use the function module START_FORM to open a form before starting the output.
  
  You must end form printing by using the function module CLOSE_FORM. Otherwise, the system does not print or display anything.
• CALL FUNCTION 'START_FORM':
  In-between the function modules OPEN_FORM and CLOSE_FORM, you can use different forms. This allows you to combine several different forms into one print output. However, you can combine only those forms that have the same page format.
  
  To switch forms, use the function module START_FORM. If another form is still open, you must close it first using END_FORM.
  
  If you specify no form name when calling START_FORM, the system restarts the last open form. If after OPEN_FORM no form was activated yet, the system leaves the function module with the exception UNUSED.
• CALL FUNCTION 'WRITE_FORM':
  The system outputs the form element specified in parameter ELEMENT into the currently opened form.

In the parameter WINDOW you can specify the name of a window for the output. Remember that the form element must be defined in this window. The parameter FUNCTION specifies how to merge the text lines to be output with any existing contents in the window. In this case, there are differences between the different window types or areas.

CALL FUNCTION 'END_FORM'
CALL FUNCTION 'START_FORM'
CALL FUNCTION 'WRITE_FORM'
CALL FUNCTION 'END_FORM'
CALL FUNCTION CLOSE_FORM