Missing api reference / documentation not clear. Whis is itemSize property?

[danierlr]

Examples page contains such code:

onst Example = () => (
  <List
    height={150}
    itemCount={1000}
    itemSize={35}
    width={300}
  >
    {Row}
  </List>
);

What is itemSize? How does it relate to height and width?