Undocumented and unuseable. The few times I have needed to use this, it's been far more trouble than it was worth. For example, how on earth can I load an arbitrary typeface? There doesn't seem to be documentation even in the C version.
I ended up doing the following procedure:
* Write a parser to break the truetype font format up
* Write a method of getting the curves out of the truetype font
* Write a drawing routines to draw the truetype font curves onto a Cairo canvas
That's how I did these illustrations, for example: