VDU 23,10 set flash rate
				VDU 23 ,11 restore default pattern-fills
				VDU 23,12
				VDU 23,13 set simple pattern-fill
				VDU 23,14 pattern
				VDU 23,15
				VDU 23,16 control cursor movement
				Functions 17 to 31 are reserved.
				Any value greater than 31 following VDU 23
				is taken as a reference to a character which is
				to be redefined.
VDU	24	X	8	Define graphics window.
VDU	25	Y	5	Equivalent to the BASIC PLOT statement
				(See Appendix 6.)
VDU	26	Z	0	Restore text and graphics windows.
VDU	27	[	0	Does nothing.
				Note that [CTRL]+ [ is equivalent to [ESCAPE„„„].
VDU	28	\	4	Define text window.
VDU	29	]	4	Define graphics origin (te. the position on the
				screen with graphics co-ordinates (0,0). For
				example:
				VDU 29,640;512;
				makes subsequent graphics co-ordinates
				relative to (640,512) --a point roughly in the
				centre of the screen.
				Note the (mandatory) use of semicolons.
VDU	38	^	0	Move text cursor to (0,0).
VDU	31	--	2	Move text cursor to a specified position
				(equivalent to PRINT TAB). For example:
				VDU 31,28,18 moves the text cursor to
				character position 20 on line 10 (the first
				character position and line being 0).
VDU	127		0	Backspace and delete (i.e. the normal action
				of [DELETE].
		App 7.4