The column files a local folder as an absolute key — `/2012` — while a frame
carries its own `dir` as a path from the root, `2012`. `shown` set the two
against each other as they stood, so a frame's dir was never the node's dir, and
never under it either: every folder in the disk tree was counted in the row
above it and stood in no pane at all — the wall white, the frames nowhere.
The key sheds the slash it leads with before the two are set against each other,
the way `markOf` already cleans a reading's own path.
Measured on the live account's own catalogue — 112761 frames, 6 under `/2012`:
the node matched 0 frames before, 6 after; the root's own list is untouched
(927).
3dtours
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