basic lines to show cut points

Hello,

out of curiosity, how could I easily overlay histograms with lines/arrows at the points where I cut for illustrative purposes. Would be curious about arrows for 1D histograms and lines for 2D histograms. For example let's say I have a 2D plot showing m1 vs m2 and I want to highlight the region which is +- 20 units from the diagonal (highlight with shading or lines parallel to diagonal or ...). Would be especially good if those would scale and zoom along with the histogram itself so their positioning is fixed to the bin location etc.

Thanks,

Mario Kadastik, PhD
Researcher

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  "Physics is like sex, sure it may have practical reasons, but that's not why we do it" 
     -- Richard P. Feynman