Having just referenced a diagram from another system, it was a good reminder that charts are abstractions that might be unfamiliar. So a Legend is often useful.
It would be nice if charts had the option to insert a (collapsible?) legend as an inset box.
And while that Contextual Family legend is comprehensive, the thought occurred that having the legend diagram a selected person in the tree instead of a dummy could open new options and or use more familiar data.
A pet peeve of mine is report identification. I believe I opened a Gramps bug report about this years ago.
Suppose you generate a cool report and a couple of cousins get a copy and pass along copies to others. All too often, those recipients lose track of who prepared the report, when, and even what it purports to represent. In my view, ALL reports should have include a block of meta-data that at least hints at these elements. Maybe a report identification block (ala architectural drawings) or just standard header/footer elements or some other approach depending on the type of report.
And while identifying the report & copyright in the Header/Footer would be a nice option, it isn’t the same as a legend. The Legend instructs users how to interpret the abstractions.