Spotlight importer: which key/value to make a file UTI seen as a "Spreadsheet" and not as "Other"

On my spreadsheet application, with its own UTI, I wrote a Spotlight importer plugin.

It works well, except that Spotlight group the found files as "Other" and not as "Spreadsheet". My UTI conforms to public.spreadsheet. Any idea?

Is there a special kMDxxx key/value to set for that in the importer?(see: https://developer.apple.com/library/archive/documentation/CoreServices/Reference/MetadataAttributesRef/Reference/CommonAttrs.html ) Thanks!

Spotlight importer: which key/value to make a file UTI seen as a "Spreadsheet" and not as "Other"
 
 
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