Steps:
Press 'Tab' key at least 10 times in 20 seconds.(Long press the 'Tab' key will be better.)
Expect results:
PASS
tabindex(omitted)
tabindex(empty)
tabindex(a)
tabindex(-1)
tabindex(0)
tabindex(3)
tabindex(2)
tabindex(2)
tabindex(2)
tabindex(1)