The column's ring was drawn from the open node's roll: a row of another roll
had no path under it, so the empty prefix matched every row of the roll being
read and the whole column lit up. The roll's own row was marked too, at every
moment of a reading of it, and a reading kept to one folder counted its frames
onto the roll's row as well — a roll counted down to one branch of itself.
A queued request was drawn from the reading's roll instead of its own, so a
request on a second roll showed nothing at all.
3dtours
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