This test confirms that selecting an element having Shadow DOM doesn't cross editing boundaries errornously.

BEFORE
AFTER
Move mouse from BEFORE to HOST
PASS selection.anchorNode is null
PASS selection.focusNode is null
PASS document.execCommand("delete") did not crash.

Move mouse from AFTER to HOST
PASS selection.anchorNode is null
PASS selection.focusNode is null
PASS document.execCommand("delete") did not crash.
PASS successfullyParsed is true

TEST COMPLETE