[CONNECT U12] (Technology Preview) Expression - Lookup Tables

Hello everyone,

Reading the online documentation about Expression, there is this phrase:


"Lookup tables are lists of data that are associated with a field in your project database, usually in excel format".


Exactly what does it means? Is there or will it be possibile to associate another type of file instead of an excel file?
If yes,what type of file?

Best Regards,

Matteo Sodomaco