I would consider this both an unimplemented-feature use-case argument, and a bug, because while 'language:C' works in both Repository and Code search mode, 'stars:>100' only works in Repository mode, yet the 'Cheat sheet' link at the bottom doesn't reflect this fact. Either the documentation needs to match the functionality, or ideally, the functionality needs to match the documentation (and intuition). :P
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FYI, this form works, you do actually get feedback :)