Introduction 2 cOnUnarids 'or the' DISPLAY EDITING SYSTEM have been , 'that the number of operations required of the. ,user'and efficiency of the editing system. For
. . , , • operations' may be and invoked as user
written EXECS or commands. • _ The CHANGE command, which allows the user to change one character
string within an item to another, also can be made to specify a horizontal "zone" within which the change is to occur, as well as both vertical and
horizontal continuation counts. Thus, the change may be made on con­
secutive items or repeatedly within the same item. • It is frequently necessary to apply a change made by cursor positioning on the display screen to several consecutive lines. The REPEAT command has
been installed for this purpose. • A facility called Screen Operation Simulation, sos, has been included to
allow the user to simulate the operation of the display terminal. Through
the use of SOS commands and the CMS console stack, the user can pre­
program the operation of the terminal to simplify repetitive or complex
actions.
Above all, the DISPLAY EDITING SYSTEM is flexible and has been designed to
allow the user to tailor his editing environment. Several components are
included in the system to facilitate this. For example: • Program Function Keys may be assigned by the user to perform any
function, or combination of functions, desired. • Optionally, at edit level initiation, a "default" EXEC can be automatically
invoked to establish a user -specified editing environment. • An SVC interface to the EDGAR command processor allows the to
write his own editing commands and invoke them during an active edit
session.

The 110 Processor
The Display Processor As shown'ih figure' i, the DISPLAY EDITING SYSTEM editor, EDGAR, is '
comprised of three major components: I/O Processor
Display Processor
Editing Command Processor
The I/O Processor maintains a storage copy of an I/O virtual screen. The I/O virtual screen has the same physical characteristics as the user's 3270 (if any)
and may be updated as a result of activity on either of two sources; the physical display device, or the Screen Operation Simulation (SOS) facility.
(The operation of Sos is described in Section v, Advanced Editing Facilities).
The operation of the I/O Processor is as follows:
1. For each edit level currently selected for display, map the corresponding
edit level virtual screen to the appropriate areas of the I/O virtual screen.
2. Allow the sos facility to update the I/O virtual screen.
3. If ENTER depressed by sos, go to step 6.
4. Replicate the contents of the I/O virtual screen on the physical display
device and wait for action by the terminal user. When user depresses a PF key or ENTER, reflect made on the physical display device to the
I/o virtual screen.
5. If ENTER not depressed by UStf, rtlufn Lo slep 2.
6. Reflect changes made to the I/O virtual screen back to the edit level
virtual screen(s).
7. Pass control to the Display Processor once for each currently displayed
edit level virtual screen. Process the edit level virtual screens in the order,
top down, that they appeared on the I/O virtual screen. Then return to Step 1.
Upon receiving control from the I/O Processor the Display Processor analyzes
the edit level virtual screen. The data and command areas are passed through
the CMS input translate table. For information on the use of the CMS input/ output translate tables, see IBM Virtual Machine Facility /370: CMS Command and Macro Reference Gc20-1818. The data file records are, then,
updated according to the changes in the data areas, and the commands are
passed, one at a time, to the Editing Command Processor. Each command is
terminated by either a X'O!' or the end of the command area on the edit level
virtual screen. Thus, through the use of the CMS input translate table, a user
may assign any character to be a logical command separator. Also, since all
data is passed through the CMS input translate table a user may enter any
character from the keyboard (or via sos) and have it appear as a different
character in the data file. System Overview 3