Hi Emilio,
I'm assuming any such how-to or wiki has not been written yet. I'll think about writing it in the future when I have time, but at the moment it's not on my immediate priorities 
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Luke's first reply is actually almost a step-by-step (albeit very high level). So, if you take that as your starting point, and look at all of the existing XML configurations that he is referencing, you could gain some understanding of the logic required to create a new analytic.
Best of luck
Matthew