The function zone compute the zone of the given x-monotone curve in the existing arrangement. Meaning, it output the arrangement's vertices, edges and faces that the x-monotone curve intersects. The order of the objects is the order that they are discovered when traversing the x-monotone curve from left to right.
A given point-location object is used for answering point-location queries during the insertion process. By default, the function uses the ``walk along line'' point-location strategy - namely an instance of the class Arr_walk_along_line_point_location<Arrangement_2<Traits,Dcel> >.
PreconditionIf provided, pl must be attached to the given arrangement arr.