[mapserver-users] overlaysymbol depreciated?

[andy]

My current maps have railroads displayed like this:

CLASS
	NAME 'Railroad'
	SYMBOL 'circle'
	COLOR 0 0 0
	SIZE 1
	OVERLAYSYMBOL 'railway'
	OVERLAYCOLOR 0 0 0
	OVERLAYSIZE 7
	STYLE
		GAP -25
	END
END

Which works.  But OverlaySymbol and friends don't seem to be documented. 
  Did they go away at some point?  What should I be using instead?

Thanks,

-Andy