https://docs.google.com/spreadsheets/d/1H9YymBrAu-ART85fzOKf52umidd1ui-lU4txOpbAC5k/edit#gid=600291584

"Make one-to-many or many-to-one mapping for each collection item. With minor refactoring at runtime side to iterate collection items, non-nested collection could be supported. However to support nested collection, we need for-loop support in expression (#1514).
Like commented in #1514, @Tomo has no idea what ""template based language"" means, how to implement and amount of effort to implement it."