I thought the find function was broken at first, because it fails silently when the search string isn't present or is before the cursor. Some feedback for those cases would be good.

This part is a nice trick:

$d->protocol(WM_DELETE_WINDOW =>[withdraw => $d]);
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It keeps the TopLevel object around even if the user deletes it. I do something similar but the other way around, binding code to <Destroy> that undefs the variable holding the window object. I don't see recreating trivial windows as having much cost.