After making a selection in Paint Shop Pro, you can move the selection anywhere on the image, including off the canvas. If you've expanded the image window to show the off-canvas diagonal crosshatch pattern area, you'd see the portion of the selection moved off the canvas. The Clip to Canvas command allows you to remove the portion of the selection not within the image borders. To use this command:
Make a selection and move part of it off the image canvas.
If necessary, expand the image window to reveal the diagonal crosshatch pattern area that appears outside the image borders.
Optionally, choose Selections > Defloat. This will defloat the selection, which allows for more selection edits than would otherwise be available. If you don't choose this command, Paint Shop Pro will display an Auto-Actions dialog, prompting you to take this action before completing the next step.
Choose Selections > Clip to Canvas. The selection area outside the image borders will be removed as shown here.