Features›Editing›Insert lines (IL)

Insert lines (IL)

Category: editing · Baseline: modern · Tags: ECMA-48 Standard, VT100 · Specification ↗

ESC [ N L

IL inserts N blank lines at the cursor row, scrolling existing lines down within the scroll region. The sequence is ESC [ N L (default N=1). Lines scrolled past the bottom margin are lost. Used by full-screen applications to make room for new content without redrawing the entire screen.

How this is testedautomated
Write 3 lines, move to row 2, send \x1b[1L (IL 1), verify row 1 is blank and original content shifted down.

The same probe runs against headless backends (via Termless) and real terminal apps (via a daemon launched in each terminal). This lets us distinguish parser correctness from rendering correctness.

Analysis2026-04-06

Supported by 11 of 12 terminals (92%). Not supported by: vt100.js. Part of the Modern TUI baseline. Notes: vt100.js: IL (insert lines) not implemented in vt100.js baseline emulator.

Supported by 12 of 14 backends (86%)

Terminal Applications

Terminal	Version	Support	Notes
iTerm2	3.6.9	✓ yes
Ghostty	1.3.1	✓ yes
VS Code		✓ yes
Warp		✓ yes
Cursor		✓ yes
Terminal.app		✓ yes

Headless Backends

Parser correctness only — a ✓ means the parser accepts the sequence.

Backend	Version	Support	Notes
Alacritty	0.26.0	✓ yes
Kitty	0.40.0	✓ yes
vterm	0.2.0	✓ yes
WezTerm	0.1.0-fork.5	✓ yes
xterm.js	5.5.0	✓ yes
vt100.js	0.2.1	✗ no	IL (insert lines) not implemented in vt100.js baseline emulator

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