To test this manually, click on "hello", and extend selection to right by pressing right arrow keys with shift twice. Then click again on "world" and extend selection twice the same way.

hello
world
PASS: mousedown
PASS: selectionchange
PASS: mouseup
PASS: click
PASS: keydown
PASS: keyup
PASS: selectionchange
PASS: keydown
PASS: keyup
PASS: selectionchange
PASS: mousedown
PASS: selectionchange
OPTIONAL: selectionchange
PASS: mouseup
PASS: click
PASS: keydown
PASS: keyup
PASS: selectionchange
PASS: keydown
PASS: keyup
PASS: selectionchange