Keep tool down

I changed the pocket operation to keep the tool down whenever possible.
I have changed the "area" module to make Subtract work again.
This is my function in area_funcs.py

def feed_possible(p0, p1):
....obround = make_obround(p0, p1, first_offset_for_pocket)
....a = area.Area(area_for_pocket)
....obround.Subtract(a)
....if obround.num_curves() > 0:
........return False
....return True

P.S. how do I get the spaces to stay at the start of the line in blogger?

Attach operation

I have added an "Attach" operation.
You select a solid before making it.
Any other operation done, after an attach operation, will have its feed moves dropped down on to the solid ( or solids ) specified by the attach operation. This can be cancelled by an "Unattach" operation.
In the picture, an existing "Pocket" operation is attached to the cone.
This is not finished yet. I need to add a "minimum z" value to the attach operation; currently it is set to 0. Also, I need to decide if the z height specified in the existing operation should be taken into account. For example, if the pocket operation is trying to cut to z-1, should I make this be 1mm below the surface contact point?