Left, Top, Right, Bottom are the selection bounds. Shape specifies the selection shape, which can be modified using ShapeModifier and ShapeAngle. Op specifies whether to add a new selection (iespAdd) or replace the current one (iespReplace).
Note: ◼SelectShape creates a "vectorized" selection (the selection will be made up of a series of lines and can be accessed via PolySel) ◼You can allow your user to make a shaped selection by enabling SelectionShape