Thanks for all that, however for the last question what I actually want to
do is shade in an arbitrary area (defined by points) which isn't defined
on the histogram. ie take the example where I have an exclusion region for
a search in 2D parameter space, and also want to shade off kinematically
excluded regions without altering the contents of the histogram. In
summary, I want to make a primitive filled area with a different shading
style to the rest of the histogram.
>
> Rene Brun
>
Thanks,
Chris.