I am attempting to do a non-standard thing, but I doubt that I am the first to come across this... Any experience out there?
What I want is to have a LINE or TEXT on a plot that has it's Y values specified in 'data' units, and it's X values in 'normalized' units.
Why? Well, the line or text is an annotation on the plot that shows the occurance of an event in the Y coord system, but I want it to show up at a fixed place in the X coord system, even when I zoom, or change the axis. (An example of this is a two sided plotyy. I want the right hand 'ticks' to be fixed to the Y values, but always be at the same spot on the graph (X), and I want to be able to zoom and do axis changes without the right hand annotation moving with it...)