The current "distance" method for a path returns a distance computed along the path and then perpendicular to the path. But, at least in the case of paths, it is often preferable to compute a "delta" distance, which would be the minimum straight-line distance assuming a diversion to reach the provided point.
A similar "distance delta" for a circle would be defined as returning a number exactly the same as is currently returned, with the understanding that the point given would be the destination and not a new waypoint. Similarly, the distance beyond the end of a path to the provided point would be counted only once, while the distance before the beginning of the path would be counted twice (one leg to the point, and the other leg back from that point to the start point (or nearest path point, if closer).
This obviously must be implemented in a backwards-compatible fashion.