apparently the diagram doesn't show in preview mode

It does for me. Can you show us the input you're trying? Perhaps it doesn't parse right.

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Occupy Babel!

I was not posting the diagram correctly in fact I prepend each line by space

That happens to me a lot in the Malkovich games if I'm cutting and pasting the diagram code from the previous post. Sometimes if I cut and paste from the thread it doesn't work, sometimes if I cut and past from the list of posts below the reply box it doesn't work, in both cases the other one works always. It's rather annoying.