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Int 10h, 13h            Write Character String                           many

    Writes a string of characters with specified attributes to any
    display page.

        Entry   AH    = 13h
                AL    = Subservice (0-3)
                BH    = Display page number
                BL    = Attribute (Subservices 0 and 1)
                CX    = Length of string
                DH    = Row position where string is to be written
                DL    = Column position where string is to be written
                ES:BP = Pointer to string to write

        Return  Nothing

    ------------------------------------------------------------------

    Note
    This service is available only for XTs dated 1/19/86 and later,
    ATs, EGAs, and PC Convertibles.

    The service has four subservices, as follows:

        AL=00h: Assign all characters the attribute in BL; do not
                update cursor
        AL=01h: Assign all characters the attribute in BL; update
                cursor
        AL=02h: Use attributes in string; do not update cursor
        AL=03h: Use attributes in string; update cursor

    In Subservices 0 and 1, all characters in the string are written
    to the screen with the same attribute-- the attribute specified in
    BL.

    In Subservices 2 and 3, the attribute byte for each character is
    found in the string itself. The string itself consists of a
    character followed by its attribute, another character followed by
    its attribute, and so on. The string is copied directly to the
    video buffer as is.

    In Subservices 0 and 2, the cursor position is not updated after
    the string is written.

    In Subservices 1 and 3, the cursor is moved to the first position
    following the last character in the string.

    Like Service 0Eh, Service 13h responds appropriately to ASCII 07h
    (bell), 08h (backspace), 10h (line feed), and 0Dh (carriage
    return). All other characters are printed.