The coordinates of a point can be expressed using the following syntax:
1) x,y
2) @length<angle (from the previous point you move to a distance using an angle)
3) @ x,y (from the previous point you move to a distance in the X axis and to another distance in the Y axis)
4) @ (previous point)
5) length (from the previous point you move to a distance using the current mouse position)
6) Coordinate specified in a coordinate reference system different from the current one