Format of ABLOCKCGA parameter block:
Offset	Size	Description	)
 00h	WORD	000Ah (length of following data)
 02h	WORD	top-left coordinate of character block
 04h	WORD	width of block
 06h	DWORD	-> block of WORDs describing characters (see #03879)
 0Ah	BYTE	length of block in characters
 0Bh	BYTE	highlight attribute
		bit 4: transparent background
		bit 5: overstrike
		bit 6: reverse video
		bit 7: underscore
SeeAlso: #03880