Understanding the Unit Cell of Wurtzite Crystal Structure: A Brief Overview

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My teacher wrote down something to day which I wish I had written down myself. It was about the crystal structure of wurtzite, which is an ABABABAB stacking of hexagonal lattices. What he wrote was two different specifications of the unit cell of wurtzite depending on which groups of elements in the periodic table were used to build the crystal.
I think the first was something like (1/3,2/3,..) and I don't remember the next one.
The reason I ask now is that I'm building a simulation of wurtzite crystals in a programme and would like to know what he meant exactly.

 

[aaaa202]

Never mind the first post. I found the numbers here on:
http://som.web.cmu.edu/structures/S014-ZnO.html
I suppose the numbers specify the position of an 0, and a Zn atom in the unit cell (the first two highlighted on the drawing going from bottom->up). But why are the coordinates of the other atoms not highlighted?