You have an iframe that contains draggable elements. You want dragging of these elements to continue even if the mouse pointer moves outside the iframe and over the parent document. You want the dragging to end when the mouse is released while the pointer is outside the iframe. You could try adding event listeners to the parent document, but that’s not possible when the two documents have differnt origins. What do you do?

Don’t call preventDefault on the mousedown event.

If the default behaviour isn’t prevented on mousedown, then when the mouse is moved outside the iframe and over the parent document, the document in the iframe will continue to recieve mousemove events.