I converted several old WMF CAD drawings to Expression format, and applied map fills. I used the tiles as paper textures. The dark shades in the tiles make transparent areas and the background shows thru. I can add various backgrounds for variation. As strokes, the white goes transparent, and the grayscale can be colorized. In erase blending, since the grayscale stroke becomes transparent, the dark shades will erase to whatever is below it on a layer.

I am using the tiles as GIFs. They work well in Xara, too.

Rich