The VDD provides the following message mode services:
VDD_Msg_BakColor
VDD_Msg_ClrScrn
VDD_Msg_ForColor
VDD_Msg_SetCursorPos
VDD_Msg_TextOut
The message mode services give the virtual shell device a way to display
messages to the user without affecting the video mode of the current virtual
machine. These services are intended to be used after the VDD has received a Begin_Message_Mode message. The VDD continues to provide message mode services until it receives the End_Message_Mode message.