by wedge they mean a diagonal surface the can be used for ojects drawn to be receding into background.
An example would be buildings in an isometric game.
Things that need adding....
1. Multiple selection
2. Rectangle selection tool
3. Mouse wheel moves tiles forward and back in space.
4. Keyboard Shortcuts
5. Light source direction control
6. Ability to make sprite emit light and color of choice.
7. Global Illumination.
8. Command to send all tiles to back (fresh slate)
9. Ability to turn off shadows on specific tiles.
10. Save states.