Can you give an example of how it would work in this case.  We do not need the comment on each line and wrapping an object for the sake of des of it seems a bit much.  The other option is something like, which is verbose but very explicit.
[
{"file_extension":"CSV", "description":"CSV file", "mimetype": "txt/csv", "alternate_values": ["alternate_input_value1", ...]}
...
]