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INT 2F - Multiplex - TesSeRact RAM-RESIDENT PROGRAM INTERFACE
        AX = 5453h
        BX = subfunction
            00h installation check
                DS:SI -> 8-char blank-padded name
                Return: AX = FFFFh installed
                                CX = ID number of already-installed copy
                           = anything else, not installed
                                CX = ID number for TSR when installed
            01h get user parameters
                CX = TSR ID number
                Return: AX = 0000h successful
                           ES:BX -> user parameter block (see below)
                           = nonzero failed
            02h check if hotkey in use
                CL = scan code of hot key
                Return: AX = FFFFh hot key conflicts with another TSR
                             otherwise safe to use the hotkey
            03h replace default critical error handler
                CX = TSR ID number
                DS:SI -> new routine for INT 24h
                Return: AX = nonzero, unable to install new handler
            04h get internal data area
                CX = TSR ID number
                Return: AX = 0000h
                            ES:BX -> TSR's internal data area (see below)
                           = nonzero, TSR not found
            05h set multiple hot keys
                CX = TSR ID number
                DL = number of additional hot keys to allocate
                DS:SI -> table of hot keys
                        BYTE  hotkey scan code
                        BYTE  hotkey shift state
                        BYTE  flag value to pass to TSR (nonzero)
                Return: AX = nonzero, unable to install hot keys
            06h - 0Fh reserved
            10h enable TSR
                CX = TSR ID number
                Return: AX = nonzero, unable to enable
            11h disable TSR
                CX = TSR ID number
                Return: AX = nonzero, unable to disable
            12h unload TSR
                CX = TSR ID number
                Return: AX = nonzero, invalid TSR number
                Note: if any interrupts used by TSR have been grabbed by
                        another TSR, the TesSeRact routines will wait until
                        it is safe to remove the indicated TSR from memory
            13h restart TSR
                CX = TSR ID number of TSR which was unloaded but is still in
                     memory
                Return: AX = nonzero, unable to restart TSR
            14h get status word
                CX = TSR ID number
                Return: AX = FFFFh invalid ID number
                           = other, successful
                                BX = bit flags
            15h set status word
                CX = TSR ID number
                DX = new bit flags
                Return: AX = nonzero, unable to set status word
            16h get INDOS state at popup
                CX = TSR ID number
                Return: AX = 0000h successful
                            BX = value of INDOS flag
            17h - 1Fh reserved
            20h call user procedure
                CX = TSR ID number
                ES:DI -> user-defined data
                Return: AX = 0000h successful
            21h stuff keystrokes into keyboard buffer
                CX = TSR ID number
                DL = speed
                    00h stuff keystrokes only when buffer is empty
                    01h stuff up to four keystrokes per clock tick
                    02h stuff up to 15 keystrokes per clock tick
                DH = scan code flag
                    if zeor, buffer contains alternating ASCII and scan codes
                    if nonzero, buffer contains only ASCII codes
                SI = number of keystrokes
                ES:DI -> buffer to stuff
                Return: AX = 0000h success
                             F0F0h user aborted with 0r reak
                             other unable to stuff keystrokes
            22h (v1.10) trigger popup
                CX = TSR ID number
                Return: AX = 0000h success, TSR will either pop up or beep to
                                   indicate that it is unable to pop up
                             nonzero invalid ID number
            23h (v1.10) invoke TSR's background function
                CX = TSR ID number
                Return: AX = 0000h success
                             FFFFh not safe to call background function
                             nonzero invalid ID number
            24h - 2Fh reserved
Note:   Borland's THELP.COM popup help system for Turbo Pascal and Turbo C
          fully supports the TesSeRact API, as do the SWAP?? programs by
          Innovative Data Concepts.

Format of User Parameter Block:
Offset  Size    Description
 00h  8 BYTEs   blank-padded TSR name
 08h    WORD    TSR ID number
 0Ah    DWORD   bitmap of supported functions
 0Eh    BYTE    scan code of primary hotkey
                    00h = pop up when shift states match
                    FFh = no popup (if shift state also FFh)
 0Fh    BYTE    shift state of primary hotkey
                    FFh = no popup (if scan code also FFh)
 10h    BYTE    number of secondary hotkeys
 11h    DWORD   pointer to extra hotkeys set by func 05h
 15h    WORD    current TSR status flags
 17h    WORD    PSP segment of TSR
 19h    DWORD   DTA for TSR
 1Dh    WORD    default DS for TSR
 1Fh    DWORD   stack at popup
 23h    DWORD   stack at background invocation

Format of TSR internal data area:
Offset  Size    Description
 00h    BYTE    revision level of TesSeRact library
 01h    BYTE    type of popup in effect
 02h    BYTE    INT 08 occurred since last invocation
 03h    BYTE    INT 13 occurred since last invocation
 04h    BYTE    active interrupts
 05h    BYTE    active soft interrupts
 06h    BYTE    DOS major version
 07h    BYTE    how long to wait before popping up
 08h    DWORD   pointer to INDOS flag
 0CH    DWORD   pointer to DOS critical error flag
 10h    WORD    PSP segment of interrupted program
 12h    WORD    PSP segment of prog interrupted by INT 28
 14h    DWORD   DTA of interrupted program
 18h    DWORD   DTA of program interrupted by INT 28
 1Ch    WORD    SS of interrupted program
 1Eh    WORD    SP of interrupted program
 20h    WORD    SS of program interrupted by INT 28
 22h    WORD    SP of program interrupted by INT 28
 24h    DWORD   INT 24 of interrupted program
 28h  3 WORDs   DOS 3+ extended error info
 2Eh    BYTE    old BREAK setting
 2Fh    BYTE    old VERIFY setting
 30h    BYTE    were running MS WORD 4.0 before popup
 31h    BYTE    MS WORD 4.0 special popup flag
 32h    BYTE    enhanced keyboard call in use
 33h    BYTE    delay for MS WORD 4.0
11 times:
        DWORD   old interrupt vector
        BYTE    interrupt number
        DWORD   new interrupt vector