I was just trying to make the point that in core CSS basic even/odd selection isn't possible, hence the :nth-child()/:nth-of-type() CSS selectors were introduced. SGML LINK doesn't have this particular problem, as it just encodes an automaton using transitions. For example, you can say

    <!link even
        x #postlink odd [ background-color=gray ]>
    <!link odd
        x #postlink even [ background-color=white ]>

where "#postlink even ..." means "upon an 'x' element, use gray and transition to the 'odd' link set", from where it transitions back to 'even' state on the next 'x' and so on, so that the current link set is toggled between the even and odd states. You can also set a state for child content with #uselink.