Below is a list of groups of signs that are translated to atomic glyphs in the font upon rendering. The motivation is that the standard interpretation of the controls is sometimes unsatisfactory. This corresponds to ligatures.json. At present, all ligatures are overlays, but later we may consider insertions as well. The translation is only effective if overlays are normalized to have narrow tall signs as first argument and wide short signs as second argument. In the future, the normalization may be different for overlays with a single sign as first argument and a single sign as second argument, by assuming the code points occur in numerical order.
One challenge is to translate any shading of the constituent signs to areas in the ligature. For this reason, each constituent sign comes with its bounding box.