Searching for wendy flag data

Is it possible in the Advanced Search to look for a specific Wendy Flag string ?

I have checked the FAQ but there is no mention of a keyword for Wendy Flags.

I tried flag="xxx" but this did not work

No. Mainly because they're not stored as strings. They're stored in the "wendy" tag as numbers. However, since the advanced search doesn't have bitwise operators, searching for them will be a bit of a faff.