pretext-repl

REPL/notebook where output cells expand without shifting cells below — zero layout shifts.

Layout shifts: 0
Cells: 0 Runs: 0 Frame-1 correct: YES Shift method: pre-reserve min-height
How zero-shift works: Before inserting output text into the DOM, the output block's min-height is set to the estimated height of that output — computed from line count (lines × 20px + 16px padding). Space is reserved first, text is revealed second. The cells below never see a DOM insertion that pushes them down.

Try: Click Run All or individual Run buttons. The layout shift counter should stay at 0. Edit code and re-run — cells below stay put. Press Ctrl/Cmd+Enter in any cell to run it.