TITLE: Grothendieck's mathematical diagram
QUESTION [19 upvotes]: I was going through this article (Who Is Alexander
Grothendieck?)(Wayback Machine) which appeared in the Notices of the AMS, and in it, there's a picture(page 936) which shows a mathematical diagram drawn by Grothendieck. I would be delighted if anyone could explain what that is.
Thanks in advance.
EDIT: The comments below suggest that the diagram is a dessin d'enfant. And even though I am by no means an expert, I somehow feel that it may not be one. I'd love some clarification on how one may call it so. Questions I want to ask now, are

Is the diagram really a dessin? Or is it something else?

Do the shaded parts of the diagram signify something? Are there any special types of dessins which have a similar a structure?

REPLY [3 votes]: Actually, this diagram appears in Malgoire's presentation Alexander Grothendieck à Montpellier (1973–1991) at 38:54.
It appears to be a diagram illustrating Grothendieck's ideas on "pseudo-droites", or pseudo-lines.  This idea is mentioned in the Esquisse, but I do not understand the mathematics behind it at all and I don't know if there has been anything published on this topic.