The `:` command line

Press : in Normal mode to enter the command line. Type, edit with <Backspace>, press <Enter> to run, <Esc> to cancel.

Built-in ex commands

Command	Aliases	Effect
`:w`	`:write`	Write current buffer to its path
`:w <path>`		Save as
`:wq`	`:x`	Write then quit
`:q`	`:quit`	Quit. Fails on unsaved changes.
`:q!`		Force quit (discards changes)
`:e <path>`	`:edit`, `:vi`, `:visual`	Open file; reuses existing buffer if one matches
`:bnext`	`:bn`	Cycle forward through buffers
`:bprev`	`:bp`, `:bprevious`	Cycle backward
`:split`	`:sp`	Horizontal split (see splits-and-tabs.md)
`:vsplit`	`:vsp`, `:vs`	Vertical split
`:close`	`:clo`	Close the active window
`:tabnew [path]`	`:tabe`, `:tabedit`	New tab
`:tabnext`	`:tabn`	Next tab
`:tabprev`	`:tabp`, `:tabprevious`, `:tabN`	Previous tab
`:tab <sub>`		Dispatcher: `:tab new`, `:tab next`, `:tab prev`
`:set <opt>[=<val>]`	`:setlocal`, `:se`	Runtime options — see table below
`:colorscheme <name>`	`:colo`	Load a colorscheme by name

`:set` options

Boolean options accept the bare name to enable, no prefix to disable, or =on/=off/=true/=false/=1/=0.

Option	Aliases	Default	Description
`number`	`nu`	off	Line numbers in left gutter
`autoindent`	`ai`	on	Copy previous line's indent on Enter / `o` / `O`
`smartindent`	`si`	on	Language-aware extra indent (requires `autoindent`)
`expandtab`	`et`	on	Tab key inserts spaces; off = literal `\t`
`tabstop=N`	`ts`, `sw`, `shiftwidth`	4	Tab display width and indent step
`syntax=NAME`	`ft`, `filetype`	auto	Per-buffer filetype override (`:set syntax=off` to disable)
`:ff [query]`		Interactive fuzzy file finder. See fzf.md. `:ff!` busts the cache.
`:highlight <text>`	`:hl`	Toggle a persistent text highlight. See highlights.md.
`:nohighlight [<text>]`	`:nohl`	Remove one highlight, or clear all if no arg.
`:LspRename <new>`	`:lsprename`	Rename the symbol under the cursor via the LSP server.
`:LspDiagnostic`	`:lspdiag`	Show the diagnostic at the cursor in the cmdline.
`:LspReferences`	`:lspref`	List references to the symbol under the cursor.
`:config show [fmt]`		Print the active config in TOML or JSON.
`:config path`		Print the loaded-from path and search list.
`:config convert <fmt> [path]`	`:config conv`	Write the active config in the chosen format.
`:config load [path]`		Reload the active file, or load a different one.

! suffix forces (e.g. :q!, :w! — though :w! isn't currently distinguishable from :w).

Tab completion

Press <Tab> while typing a : command to complete.

File-path completion

When the cursor is past the first space, <Tab> completes filesystem paths:

First <Tab> inserts the first matching entry (sorted alphabetically).
Second <Tab> opens a popup listing every match with the first one highlighted.
In the popup:
- <Down> / <Up> / <Tab> — navigate selection (input updates live).
- <Enter> — accept selection and run the command.
- <Right> — accept selection, stay in command mode.
- <Left> — close popup, discard completion state.
- Any other typed key — close popup, resume normal cmdline editing starting from the current selection.
Directory matches are completed with a trailing / so you can keep drilling in. Pressing <Tab> again on :vi src/ descends into src/ and lists its contents (instead of just re-showing src/).
~/ is expanded to $HOME for that segment.

Command-name completion

When the cursor is BEFORE the first space (still on the command name), <Tab> completes ex command names from the registry — including aliases:

:vspl<Tab>     → :vsplit          (only match)
:tab<Tab>      → :tab, then <Tab><Tab> opens popup with
                 tab, tabnew, tabe, tabedit, tabnext, tabn,
                 tabprev, tabp, tabprevious, tabN
:tabe<Tab>     → tabe, tabedit

Same popup UX as file completion.

How each command declares its argument completion

Every command's ExCommand::complete_arg returns an ArgCompletion value describing what Tab should resolve at a given positional slot. The variants:

None — Tab is a no-op (zero-arg commands like :q, :bnext).
Path — filesystem completion (:e, :w, :tabnew).
Enum(&[…]) — fixed list (:config show <Tab> → json / toml).
Dynamic(fn) — runtime-resolved list, for things like a future :colorscheme <Tab> that needs editor state.

The completion module dispatches through the registry, so adding a new ex command with custom completion is a single-file change: add the struct, override complete_arg, register it. Existing examples worth copying from:

:config <Tab>      → conv | convert | load | path | show
:config sh<Tab>    → show
:config show <Tab> → json | toml
:config load <Tab> → filesystem paths
:tab <Tab>         → close | new | next | prev
:tab new <Tab>     → filesystem paths

When does completion NOT trigger?

The partial input matches no entries → <Tab> is a no-op (no popup, no insertion).
Typing any character clears the active completion cycle.

Search line (`/` and `?`)

Keys	Action
`/`	Forward search prompt
`?`	Backward search prompt
`<Enter>`	Run search; cursor jumps to first match
`<Esc>`	Cancel — no pattern stored
`<Backspace>`	Edit; empty + backspace cancels

The pattern is a full Rust regex crate regex. The last pattern is remembered for n / N in normal mode.

Custom commands

The ExCommand trait is the extension point. Implement it, register the result via editor.commands.register(Arc::new(...)) in your build, and it becomes available at runtime. See extending.md for the trait shape and an example.

Plugin-style external commands aren't supported in v1 — there's no scripting runtime — but the registry pattern means adding the plumbing later is purely additive.

The : command line