Bounding Box Overlap

Given a main axis-aligned bounding box (x1, y1, x2, y2) and a list of other axis-aligned bounding boxes, write a function that computes the total area inside the main bounding box covered by the union of the other boxes. Boxes may overlap (overlapping regions should only be counted once), and boxes may lie partially or completely outside the main bounding box (only the portion inside the main bounding box should be considered).