worlds

This list isn't used yet in LDtk (so for now it's always empty).

In current version, a LDtk project file can only contain a single world with multiple levels in it. In this case, levels and world layout related settings are stored in the root of the JSON. after the "Multiple worlds" update, there will be a worlds array in root, each world containing levels and layout settings. Basically, it's pretty much only about moving the levels array to the worlds array, along with world layout related values (eg. worldGridWidth etc).