Drawing arcs in cairo

I'm trying to teach myself basic cairo programming but I have got stuck on arcs. The official cairo manual says:
Quote:

Angles are measured in radians. An angle of 0.0 is in the direction of the positive X axis (in user space). An angle of M_PI/2.0 radians (90 degrees) is in the direction of the positive Y axis (in user space). Angles increase in the direction from the positive X axis toward the positive Y axis. So with the default transformation matrix, angles increase in a clockwise direction.

This seems to me contradictory, both in itself and with my experiments. If (+)M_PI/2 is the positive Y-axis, then an arc from 0 (the positive X axis) to M_PI/2 should go anti-clockwise, i.e. above the X-axis. But it does in fact go clockwise underneath the X-axis. What am I missing?