[matplotlib-devel] constrained zoom

One more thought on interactive zoom.  As I was trying out the
interactive zoom (not zoom to rect, but right click on pan zoom) on
some image data, I noticed that it would be useful to have some
constraints on the zoom

  - zoom only on x.  Already the x zoom is determined by the amount of
    movement in the horizontal direction, but it would be nice to be
    able to ignore the y direction.  Candidate key modifier: 'x'

  - zoom only on y.  ditto. Candidate key modifier: 'y'

  - preserve axes aspect ratio.  Candidate key modifier: ??.  I think
    some apps use a SHIFT or a CTRL modifier for this.  Is there any
    consensus or common practice?

JDH