To build a folly is essentially to do something a second time, something at an inopportune moment. That something is always the memory of something forgotten, about which we can paradoxically say "There it is again."
Follies were misunderstood, purposeless constructions. They were often only small, extravagant gestures in a garden, easily whisking off the imagination to distant lands, a sort of time capsule built to awaken the memory and induce surprise in passers-by. They marked locations, organized secondary paths in a park, or simply predicted the arrival of better times—a demarcation, a sacred spot, a mysterious trail, a hill whose tragic rocky nature begged for a tower, a party, or the arrival of summer.
“It is demonstrably true that things cannot be other than as they are. For, everything having been made for a purpose, everything is necessarily for the best purpose.” — Professor Pangloss
Generally speaking (and ignoring questions of styling, API availability, etc.), an ideal Web annotation pattern follows these principles:
Annotations appear in close visual proximity to the primary content.
Their design neither distracts from nor hides the primary content.
The preceding principles are followed regardless of screen width.
The only pattern I’ve found that meets these criteria is FiveThirtyEight’s.
...As it turns out, FiveThirtyEight didn't invent this pattern. It likely originated in medieval illuminated manuscripts which contain “interleave notes” — comments written literally between the lines.