How can I search for code fragments on github.com? When I search for MSG_PREPARE in the repository ErikZalm/Marlin github shows up nothing.

I'm using the repository code search syntax described on https://github.com/search with 

repo:ErikZalm/Marlin MSG_PREPARE

No results, but MSG_PREPARE can be found inside this repository here. Am I missing something? Is there no code search on github.com?

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