CreateCanvas

Could someone tell me what the Style parameter is for on the CreateCanvas function? Also if you use Graphics, or CreateGraphics you can define the depth and refresh rate - is there a way to do this with a canvas graphics (or is it not relevant)?

Const GRAPHICS_BACKBUFFER= $2
Const GRAPHICS_ALPHABUFFER= $4
Const GRAPHICS_DEPTHBUFFER= $8
Const GRAPHICS_STENCILBUFFER= $10
Const GRAPHICS_ACCUMBUFFER= $20

I assume it does all of these I know it does backbuffer
doc's a little scant here...