Finding Graphviz Visual Editor very useful. First of a short set of queries.
Is there a way to move the contents of the graphic (right-hand) window around? I know how to zoom in and out, but haven’t figured out how to move the image left-right, up-down.
Hold Ctrl down and drag with the primary mouse button.
For more, click the help icon rightmost in the toolbar: 
Thanks. I’m a native English speaker and didn’t catch the intent of “pan” in the help file; I’d have found “scroll” more intuitive. A data point for your collection.
OK. Thanks. I’m not a native English speaker so I don’t really know, but it seems to me that pan and zoom is the established vocabulary. The underlying mechanism is from this D3 plugin:
Pan is definitely not wrong. But in my experience the word’s most common use by far is for wide (left-right) viewing, as in panorama; the dictionaries I checked listed this horizontal usage first. That’s probably why I didn’t pick up on the description when looking for all-direction motion. As insurance for any others out there like me, perhaps consider “Pan the graph left-right and up-down”, of “Pan the graph in any direction”?
Then some other user can complain to you that the revised description is, technically, redundant. Send them to me and we’ll fight it out. 
I don’t have any light to shed on this, but I would still like to talk about it. It was surprising to note that in photography, one talks about pan-tilt-zoom (for example in remotely operated video cameras), so X and Y are different. In computer graphics, though, according to Wikipedia, which points to some other reference I never heard of, pan means to move the camera parallel to the view plane. This doesn’t mention limiting translation to the X coordinate. I think d3-zoom also adopts this terminology.