FileList with custom setQuery

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Hi,

I'm trying to write a search that will work on both file data and the file set they are grouped by, so a search for Art would display all the art in the Art file set, and if that file set is not found, it will display all the files with the tag containing Art.

What does FileList expect out of the setQuery? I tried running a getQuery on fileList:
$testList = new FileList();
$query=$fileList->getQuery();

However, $query is blank.