[feature request] option to disallow crossing monitors

An option (when holding down Left Click and thus making a selection) to not allow the cursor to cross over to another monitor would be great for my use case.

I never really take screenshots which cross over multiple monitors, and being able to snap the cursor to the top corner of a monitor when i take a screenshot would also be useful.

The issue requests a selection option that prevents the cursor from crossing monitors and snaps it to a monitor corner. Start by reviewing the repository's command-line option handling and region-selection flow, then define the behavior for multi-monitor selections. Done means the option preserves selection within one monitor while existing behavior remains unchanged when it is not enabled.

Written by the indexing model from the issue text.