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  Using the routines:
 
     The mouse is useful for applications that require users to select
     from a list of options or move objects around on the screen.
 
     To use these routines, you must add the necessary 'DEVICE=...'
     statements in your CONFIG.SYS file.
 
     You must hide the mouse during the execution of any ANSI ACCEPT
     or DISPLAY statement that operates on the area of the screen
     where the mouse pointer is located.
 
     The attributes referred to in the descriptions of routines are
     screen attributes, not user attributes. The top left-hand corner
     of the screen is row 0, column 0.
 
  Events:
 
     Whenever the mouse is moved or a button on the mouse is pressed
     or released, the mouse hardware causes an interrupt. The mouse
     device driver takes control and, depending on a mask you have
     set, either saves it in a queue or ignores it. This prevents
     events being lost if a subsequent interrupt occurs before the
     application has read the event. With the mouse routines, you can
     read the event queue and determine how many events are in the
     queue.
 
     When an event is generated, a description of it is stored in a
     data structure called the event-data. If the mask allows (see
     below), this is added to the queue. The layout of event-data is:
 
         event-type           PIC X(2) COMP-X.
         event-time           PIC X(4) COMP-X.
         event-row            PIC X(2) COMP-X.
         event-col            PIC X(2) COMP-X.
 
     where:
 
     event-type    is the action (that is, change of state) that took
                   place:
 
                       bit 3 set = button 3 pressed
                       bit 2 set = button 2 pressed
                       bit 1 set = button 1 pressed
                       bit 0 set = mouse moved
                       (other bits are reserved.)
 
                   A button release is indicated by the bit for that
                   button changing from 1 to 0. For example, if the
                   mouse moves and button 1 is pressed at the same
                   time, event-type contains 3.
 
     event-time    is the time elapsed between when the event took place
                   and some arbitrary but fixed starting time.
 
     event-row     together, give the position of the mouse when the
     event-col     event took place.
 
  The Event Mask:
 
     The event mask, which the programmer supplies, tells the system
     which kinds of event should be queued and which ignored. It has
     the same structure as event-type. An event is queued only if it
     happens while the corresponding mask bit is on, or while another
     state is on whose mask bit is on. When an event-data is queued,
     the bit for each state is set correctly; that is, the mask does
     not mask them out.
 
     For example, the operator moving the mouse will generate an event
     if either the mask bit for "mouse moved" is off or the operator is
     holding down a button and the mask bit for that button is off.
                                    -♦-