Modifier Keys

Certain tools have different modes that can be toggled by holding Left Control / Right Control, Left Shift / Right Shift and Left Alt / Right Alt or a combination of these keys. Build and Plan tools have the following modes:
Left Control / Right Control -> Draw Line
Left Shift / Right Shift - Draw Circle
Left Alt / Right Alt - Pencil (free draw)
Left Control / Right Control + Left Shift / Right Shift -> Bucket Fill
Left Control / Right Control + Left Alt / Right Alt -> Delete (rectangle area)