INT 6F - 10NET v5.0 - CHAT
        AH = 8Ah
        DS:BX -> chat parameters (see below)
        DS:DX -> chat message (see below)
Return: CF clear if successful
        CF set on error
            AX = status (see AH=00h)
SeeAlso: AH=0Ah

Format of chat parameters:
Offset  Size    Description
 00h  8 BYTEs   sender's user name
 08h  8 BYTEs   destination user name
 10h 15 BYTEs   destination node (0 if broadcast-style chat)

Format of chat message:
Offset  Size    Description
 00h    WORD    message length
 02h  N BYTEs   chat message contents

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