Graph Discussion (Temporary)

Since commenting directly on lines in github is easier than anything else I can think of, I'm opening this PR to pass feedback to @mtbc. I've marked it "exclude" and it will likely be closed quite soon. ~Josh.

--exclude
This one was an interesting one. I made a start but found that I was usually writing text that was less clear than the actual rule it described. I could have another go, though, at least for some: it is okay if the lines end up really long? (Even I usually try not to push past 132 characters. (-:)