TileTransitions properties missing descriptions

[JohnTheCF]

https://wiki.factorio.com/Types/TileTransitions
Mandatory properties are not always mandatory and their optionality is actually determined by bool property. They are mandatory by default though. Other optional properties have no description at all (with rare exceptions) and it's not clear what _effect_map and _weights do, as well as can you set "<property>" and "<property>_mask".