:first-child :first-of-type :only-child
:last-child :last-of-type :only-of-type
:nth-child :nth-of-type
:nth-last-child :nth-last-of-type
::first-letter ::first-line ::first-word
::last-letter ::last-line ::last-word
::nth-letter ::nth-line ::nth-word
::nth-last-letter ::nth-last-line ::nth-last-word