Class used to allow GraphicsWidgets to anchor to a specific position on their parent.
Anchors the item at its local itemPos to the item’s parent at parentPos. Both positions are expressed in values relative to the size of the item or parent; a value of 0 indicates left or top edge, while 1 indicates right or bottom edge.
Optionally, offset may be specified to introduce an absolute offset.
Example: anchor a box such that its upper-right corner is fixed 10px left and 10px down from its parent’s upper-right corner:
box.anchor(itemPos=(1,0), parentPos=(1,0), offset=(-10,10))