An edit's pass waits for 300 ms of quiet instead of running between keys, so
while the typing goes on only the keystroke itself costs. When the quiet comes,
edits that only put text into one textblock and left the content's bottom where
the last pass had it skip the pass: the block is as tall as before, so nothing
below it moved. A break inside the block still runs it. Measured at the top of
a 124-page document: 41 ms a keystroke in Chromium, no pass for a letter typed
and taken back. The dom run holds both.