pdfcanvas.js getCoords_ help

[SPlatten]

What is the matrix in:

    contextPrototype.getCoords_

This is a 3 x 3 matrix, where the passed x and y are used to obtain the coordinates used for the text, but I just don't understand what is going on?

I'm trying to figure out why the coordinates returned by the module do not match those I see in GIMP, can anyone help?