Commutator Diagrams about xaml-math

[ForNeVeR]

I am not against that, but note that this would require some work in the area XAML-Math is lacking the most: drawing of vector lines and figures between arbitrarily placed blocks.

Also, I'm not sure about including this (if it's not directly related to any other known LaTeX implementation) in the default set of commands, though we eventually want to allow user-provided plugins and packages extending XAML-Math.

(since we have no extension mechanism in place for now, if any contributor implemented that, I think it would be okay to include it for now, until we've added such a mechanism)

If you are looking to implement this, then take a look at how the MatrixAtom is implemented. It is one of the most complex implemented atoms, and it does some things to calculate custom positioning for the nested atoms (i.e. the matrix cells).

Horizontal and vertical arrows would be pretty easy to add, though I'm not sure about the diagonal ones. The arrowheads may be drawn using a set of custom font glyphs (so you'd need to bundle a special font for several glyphs specifically, though at least we already support that and bundle several different fonts). And for diagonal/vertical lines, I think you'd also need an ability to rotate the glyphs (we currently don't have it, but it's possible to add).