filename:"*.ext*"

resource:application/vnd.ms-excel for .xls
resource:application/*
resource:application/pdf
resource:image/png
resource:image/gif
resource:image/*

- Search for PDF: resource:application/pdf
- Search for Doc files: resource:application/msword (does not find .docx files)
- Search for Excel files: resource:application/vnd.ms-excel
- Search for XLSX files: resource:application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
- Search for Word files: resource:application/msword
- Search for Zip files: resource:application/x-zip-compressed
- Search for specific filenames: filename:xyz* This will find filenames that start with "xyz".

One thing you can do to explore is to take a note that has an attachment you're interested in and export it to enex. Then open that file in a plain text editor (e.g. notepad). Look for a line that contains something like
application/vnd.ms-excelPlaying with Amortization Numbers.xlstrue

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