RFC 191 (rfc191) - Page 2 of 4

Graphics implementation and conceptualization at Augmentation Research Center

a rectangular "display area". A program treats this display area
much like it would a file which it has opened with write access.

When requesting the allocation of a display area, a program
specifies its attributes, including where it is to be on the
screen. The program is returned an identifier which it
subsequently uses to manipulate images within the display area
and the display area itself. Each string which the program
writes into the display area is also given an identifier, which
can subsequently be used to move, delete, replace, or change the
characteristics of that string.

   The currently implemented characteristics are character size,
   horizontal spacing between characters, and font of the
   characters (e.g. blinking, italics, intensity, etc.).

   The position of items in the display area are given relative
   to the 0,0, which is the lower left corner of the display
   area.  The horizontal coordinate increases to the right and the
   vertical coordinate increases toward the top.

In addition to above described manipulation of strings within
display areas a program can suppress the display of individual
strings within display areas or suppress whole display areas.

Also, a program can switch the terminal's state from teletype
simulation to display mode and vis versa.

   When in display mode, the teletype simulation display area is
   suppressed and the coordinates of the cursor are input with
   each character. When in teletype simulation mode, all user
   owned display areas are suppressed and the coordinates of the
   cursor are not input with each character.

At TENEX startup time, display areas are allocated for a teletype
simulation and a cursor for each local display terminal. Programs
can change the string being displayed as the cursor to give the
human feedback as to the programs state.

Within NLS:

   The NLS subsystem deals only with the cursor and the display
   areas it has requested from the system for output to the user.
   The display area formatters assumes that the display has 64K
   by 64K addressable points (with 0,0 at upper left), several
   different character sizes and fonts, and 7-bit ASCII.