As an Atlas map user both embedded in syndesis or standalone,
A. I would like to be able to map nested collections. (Not related to Expression Mapping)
B. I would like to be able to map partial collections. (Many to Many)
C. I would like to map a collection from any level in my source to any level in my target. (Example Required)
D. I want to be able to map one collection to another. (Many to Many)
E. I want to be able to map source collection field.

A and E can be considered "just" enhancements (and depend https://github.com/atlasmap/atlasmap/issues/890)
B,C,D are indipendent advanced features.

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Epic Brief: https://docs.google.com/document/d/1ZQmZD4M6llnoWzC4gEf5LxQIaCcMs2TwtQVa_hTpoLo/edit?usp=sharing

Example mappings: https://docs.google.com/spreadsheets/d/1H9YymBrAu-ART85fzOKf52umidd1ui-lU4txOpbAC5k/edit#gid=0