qxcaxis(y0, xx, xl) places labels xl at locations xx, but places ticks between labels rather than at the labels. First and last ticks are extrapolated.
qxcaxis(y0, [x0 x1], xx, xl) specifies those end ticks explicitly.
qxcaxis(..., ttl) adds a title to the axis.
qxcaxis obeys settings from qticklen, qtextdist, and qaxshift.
qxcaxis('t', ...) inverts the sign of these settings.