Comment 5 for bug 465571

I suppose the first reference would be http://en.wikipedia.org/wiki/Datamatrix

And no, the user selects the size of the matrix. If it is too small, the script will generate multiple datamatrices to hold the data.

As for the positioning, the standard extension behaviour seems to be to place in the centre of the screen. As datamatrices are always a fixed aspect ratio (most are square), I tihnk it is easier to just specifiy the module (little squares) size.