First argument:
| AllRats | Create rat lines for all loaded nets that aren't already connected on with copper. | 
|---|---|
| SelectedRats | Similarly, but only add rat lines for nets connected to selected pins and pads. | 
| Close | Selects the shortest unselected rat on the board. | 
The second argument is temporary and optional, for a workaround of a bug in the old (to be removed) autorouter. If the value of the second argument is "manhattan", non-axis-aligned lines are ignored when looking for rat anchor points.