In Yannis Haralambous' Fonts and Encodings
, he gives an example of an OpenType single adjustment positioning:
It's pedagogically a very neat example of how GPOS and OT features work: you put a simple positioning rule inside a feature (
); turn on the feature and the parentheses drop down vertically.
But has this (or anything like it) been seen in fonts in the wild? Does it even make typographic sense?