Feature Audit

This page is the enumeration ("洗い出し") phase: a systematic sweep of the capability space of a terminal toolkit, cross-referenced against the established libraries in the field (notcurses, crossterm, tcell/termbox, blessed, Python rich/prompt_toolkit, ncurses), with each capability marked against cl-tty-kit's actual public API. This page is the canonical copy; the former docs/FEATURE-AUDIT.md duplicate is gone.

Status legend:

• DONE — implemented and tested in the public API.
• GAP — a reasonable, in-scope capability that was missing; addressed in the "wave 5" pass unless noted.
• DEFERRED — intentionally out of scope for now, with a rationale. These are also recorded in Roadmap.

The guiding constraint (see Roadmap) is terminal primitives, SBCL-only, small and testable — not an application framework. "Comprehensive" is measured against that boundary, not against full terminal emulation.

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A. Terminal I/O and modes

Capability	Status	Notes
Raw mode (enter/leave, nesting)	DONE	enable-raw-mode, disable-raw-mode, with-raw-mode — see Terminal Session
Alternate screen buffer	DONE	ansi-enter-alternate-screen, ansi-exit-alternate-screen
Terminal session lifecycle	DONE	with-terminal-session
Cursor show/hide	DONE	ansi-hide-cursor, ansi-show-cursor
Bracketed paste mode	DONE	enable/disable + streaming collection — see Input Decoding
Focus reporting	DONE	enable/disable + :focus-in/:focus-out decode
Mouse tracking modes	DONE	ansi-enable-mouse/-disable-mouse (:normal/:button/:any + SGR) — see Mouse Input
Kitty keyboard enhancement	DONE	ansi-set/push/pop-keyboard-enhancements
Cursor position query	DONE	ansi-request-cursor-position + decode-cursor-position-report
Terminal bell	GAP → DONE	ansi-bell
Synchronized output (DEC 2026)	GAP → DONE	ansi-begin-synchronized-update/-end-synchronized-update (flicker-free repaints)
Terminal soft reset	GAP → DONE	ansi-reset-terminal (RIS)
Runtime terminal size	GAP → DONE	terminal-size (ioctl TIOCGWINSZ; returns NIL off a tty)
PTY window-size propagation	DONE (third pass)	pty-resize — see PTY

B. ANSI escape building

Capability	Status	Notes
Clear screen / line (with modes)	DONE	ansi-clear-screen, ansi-clear-line
Absolute cursor move	DONE	ansi-move-cursor, ansi-cursor-column
Relative cursor move	DONE	ansi-cursor-up/-down/-forward/-back
Save / restore cursor	DONE	ansi-save-cursor, ansi-restore-cursor
Scroll up/down + scroll region	DONE	ansi-scroll-up/-down/-set-scroll-region
Window title	DONE	ansi-set-window-title
Cursor shape	DONE	ansi-set-cursor-style
SGR text attributes	DONE	bold/dim/italic/underline/blink/reverse/hidden/strikethrough + generic ansi-sgr
SGR reset	DONE	ansi-reset-style
Default fg/bg (SGR 39/49)	GAP → DONE	ansi-default-foreground, ansi-default-background
OSC 8 hyperlinks	DONE	ansi-hyperlink
256-color / truecolor SGR	DONE	via the style model + style-ansi — see ANSI Helpers

C. Input decoding

Capability	Status	Notes
Printable / control / Alt-prefixed keys	DONE	decode-input, decode-key-sequence
Named special & function keys (CSI / SS3 / CSI-u / kitty)	DONE	key tables
Modifier decoding & normalization	DONE	shift/alt/control
Streaming / chunked decode	DONE	make-input-decoder, decode-input-chunk, flush-input-decoder
Bracketed paste (streaming)	DONE	:paste events / marker events
SGR mouse (press/release/drag/move/wheel)	DONE	decode-mouse-sequence + inline via decode-input
Focus in/out	DONE	:focus-in/:focus-out
Cursor position report	DONE	standalone decode-cursor-position-report
Human-readable key labels	DONE	key-event->string
Device attributes (DA) response decode	DONE (third pass)	ansi-request-device-attributes + decode-device-attributes

See Input Decoding and Mouse Input for the full API.

D. Unicode and text measurement

Capability	Status	Notes
Per-character terminal column width	DONE	char-width (zero/one/two-width via sb-unicode)
String column width	DONE	string-width
Width-aware truncation (+ ellipsis)	DONE	truncate-string
Width-aware padding / alignment	DONE	pad-string
Word wrapping (+ hard split)	DONE	wrap-string
Grapheme-cluster segmentation	DONE (fourth pass)	string-graphemes, grapheme-count, grapheme-width via sb-unicode:graphemes

See Text Layout for the full API.

E. Screen / cell model

Capability	Status	Notes
Fixed grid of styled cells	DONE	screen, cell, make-style
Cell/style construction & normalization	DONE	style-fg/-bg, make-style, style-merge, style-ansi
Put / fill-rect / write-string	DONE	width-aware screen-write-string
Whole-grid fill	DONE	screen-fill
Deep copy / region blit / scroll	DONE	screen-copy, screen-blit, screen-scroll
Row / whole-screen text extraction	DONE	screen-row-string, screen-to-string
Multi-line / wrapped / aligned placement	DONE	screen-write-lines/-wrapped/-aligned
Blank-cell predicate	DONE	cell-blank-p
Resize preserving content	DONE	screen-resize
Region extraction	DONE (second pass)	screen-crop

F. Rendering

Capability	Status	Notes
Full repaint	DONE	render-screen
Minimal diff repaint	DONE	render-diff (clear-line runs, dimension-aware)
Cursor render	DONE	render-cursor
Frame (screen + cursor)	DONE	render-frame, render-frame-diff
Double-buffered render loop	DONE	renderer (renderer-render emits only changes + snapshots)
Synchronized-update wrapping	DONE (B)	ansi-begin/end-synchronized-update can bracket a renderer-render

See Screen and Rendering for the full API.

G. Color

Capability	Status	Notes
16 named colors → index	DONE	named-color
Hex parse (#rrggbb / #rgb)	DONE	parse-hex-color
xterm-256 ↔ RGB	DONE	color-256-to-rgb, rgb-to-256
RGB blend / gradient ramp	DONE	blend-colors, color-gradient
RGB → nearest 16-color	GAP → DONE	rgb-to-ansi16 (for low-color terminals)
Perceived luminance	GAP → DONE	color-luminance (e.g. to pick readable fg over a bg)
HSL / HSV round-tripping	DONE (second pass)	rgb-to-hsl/hsl-to-rgb, rgb-to-hsv/hsv-to-rgb
Unified color parsing	DONE (second pass)	parse-color (hex / rgb(...) / name), contrast-color

See Color for the full API.

H. Layout geometry

Capability	Status	Notes
Rect value + accessors	DONE	rect, make-rect, rect-x/y/width/height
Inset (margins)	DONE	rect-inset
Horizontal / vertical split	DONE	rect-split-horizontal/-vertical
Point-in-rect	DONE	rect-contains-p
Emptiness / area	GAP → DONE	rect-empty-p, rect-area
Intersection / union	GAP → DONE	rect-intersect, rect-union (clipping & damage bounds)
Constraint-based layout split	DONE (fourth pass)	layout-split (ratatui-style :length/:percentage/:ratio/:min/:fill)
Full flex/grid constraint solver (Cassowary)	DEFERRED	application-framework territory; layout-split/rect-inset cover panel layout

See Layout for the full API.

I. Widgets and formatting

Capability	Status	Notes
Box borders + lines (5 styles)	DONE	screen-draw-box, screen-draw-horizontal-line/-vertical-line
Box title	GAP → DONE	screen-draw-box :title/:title-align
Progress bar (sub-cell)	DONE	format-progress-bar
Sparkline	DONE	format-sparkline
Aligned columns (single row)	DONE	format-columns
Multi-row table (auto widths)	GAP → DONE	format-table
Spinner frames	GAP → DONE	spinner-frame
Bitmap graphics (sixel)	DONE (fifth pass)	format-sixel

See Widgets for the full API.

J. PTY / process

Capability	Status	Notes
Spawn under PTY	DONE	make-pty
Read / write / close	DONE	pty-read, pty-write, close-pty
Window-size propagation	DONE (third pass)	pty-resize
Fd-centric byte-transparent I/O (multiplexer use)	DONE	pty-fd, pty-pid, fd-read-octets, fd-write-octets

See PTY for the full API.

K. Embedded logic engine

Capability	Status	Notes
Unification + CPS resolution + clause DB	DONE	nerima-lisp/cl-prolog, a test-suite dependency (differential-testing oracle)

See Logic Engine for the full API.

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Second pass — competitive research (2026-07-20)

The first pass above was from domain knowledge. To make the enumeration genuinely comprehensive rather than recalled, a second pass surveyed the actual published capability surfaces of the major terminal libraries — crossterm/ratatui (Rust), notcurses (C), tcell/termbox2 (Go), and rich/prompt_toolkit/blessed (Python) — and diffed each capability against the then-current public API. The diff surfaced primitives that appeared across two or more of those libraries but were missing here. All of them were then implemented:

• Style / SGR — extended underline styles :double-underline, :curly-underline, :dotted-underline, :dashed-underline (SGR 4:2..4:5), :overline (SGR 53), and a separate underline color via style-underline-color (SGR 58). (crossterm, notcurses, termbox2, rich.)
• Color — rgb-to-hsl/hsl-to-rgb, rgb-to-hsv/hsv-to-rgb, a unified parse-color (hex / rgb(...) / name), and contrast-color. (ratatui, rich, termenv.)
• ANSI / OSC — ansi-set-clipboard (OSC 52, base64), ansi-set-palette-color (OSC 4) / ansi-reset-palette (OSC 104), ansi-request-foreground-color / ansi-request-background-color (OSC 10/11) with decode-color-report for the reply, ansi-enable-line-wrap / ansi-disable-line-wrap (DECAWM), and ansi-cursor-next-line / ansi-cursor-previous-line (CNL/CPL). (notcurses, crossterm.)
• Unicode / text — East Asian Ambiguous width policy (*east-asian-ambiguous-wide*), expand-tabs, chop-string (hard column chop), and strip-ansi (sequence-aware measurement). (notcurses, prompt_toolkit, rich, blessed.)
• Screen — screen-crop (extract a rect region as a new screen). (rich set_shape, ratatui.)
• Input — horizontal wheel :wheel-left/:wheel-right in mouse decoding. (crossterm ScrollLeft/Right.)

Third pass — closing the feasible deferrals (2026-07-20)

A review of the second-pass "Deferred" list separated items that were genuinely out of scope from ones deferred only for expected effort. The feasible ones were then implemented:

• Kitty keyboard event kinds — key-event-kind (:PRESS / :REPEAT / :RELEASE), decoded from the CSI-u (and general CSI) MODIFIER:EVENT sub-parameter, so every key event now carries its kind (default :PRESS off the kitty protocol).
• Extended named keys — the kitty private-use function/keypad/media codes were already tabled; added the legacy CSI-tilde codes for F13–F20.
• Reverse ANSI parsing — decode-sgr (an SGR escape → normalized style, the inverse of style-ansi) and parse-styled-string (a styled string → a list of (text . style) segments, accumulating style across sequences via style-merge).
• Device Attributes — ansi-request-device-attributes (DA1) and decode-device-attributes for the ESC [ ? ... c reply.
• PTY window-size propagation — pty-resize (ioctl TIOCSWINSZ on the PTY's descriptor). Implementing this also surfaced and fixed a latent bug: terminal-size had been calling a hand-declared ioctl alien routine, which on the arm64 variadic ABI passes the winsize pointer in a register instead of on the stack, so the ioctl always failed with EFAULT and the function silently returned NIL. Both now go through sb-unix:unix-ioctl, which marshals correctly; terminal-size actually reports the size now (verified by a pty-resize → terminal-size round-trip in the tests).

Fourth pass — re-examining two more deferrals (2026-07-20)

Two items previously deferred turned out to be feasible after a closer look:

• Grapheme-cluster segmentation — it was deferred on the assumption it would require shipping Unicode grapheme-break tables. In fact sb-unicode:graphemes is already in the SBCL image, so string-graphemes, grapheme-count, and grapheme-width were added for free. (SB-UNICODE's graphemes errors on the empty string; that edge is guarded.)
• Constraint-based layout — a full Cassowary solver is application territory, but the practical ratatui-style constraint split is a geometry primitive: layout-split divides a rect along an axis by a list of (:length N), (:percentage P), (:ratio A B), (:min N), and (:fill WEIGHT) constraints (with spacing), sharing leftover space by weight via largest-remainder.

Fifth pass — closing the remaining feasible items (2026-07-20)

• Kitty associated text — the CSI-u text field (field 3) is now decoded into key-event-text (the string a key inserts, for IME/international input), and the shifted-key subfield of field 1 is skipped to the primary key. Combined with key-event-kind, the practical kitty input surface is covered.
• In-place editing escapes — ansi-insert-line/ansi-delete-line (IL/DL), ansi-insert-char/ansi-delete-char/ansi-erase-char (ICH/DCH/ECH), ansi-cursor-row (VPA), and ansi-repeat (REP) round out the CSI editing set that terminal libraries use for partial-line updates.
• Sixel graphics — format-sixel encodes a raw RGB pixel buffer into a sixel DCS string (xterm-256 quantization, 6-row bands, run-length compression), so a sixel-capable terminal can render bitmaps. This closes the "graphics" gap for the widely supported sixel format.

Also closed the last decodable kitty field: the CSI-u first field's shifted and base-layout key alternates now populate key-event-shifted-key and key-event-base-key (for layout-independent keybindings), completing the kitty input surface.

A follow-up sweep of the ANSI mode surface added the generic ansi-set-mode / ansi-reset-mode (DECSET/DECRST/SM/RM by number) — the base primitive the specific ansi-enable-* toggles specialize, so the long tail of DEC private modes this library does not individually wrap (1047, 47, 12, 1005, 1015, 1016, ...) is now reachable — plus ansi-reset-scroll-region. (Hardware tab stops and SCS character-set designation were considered and left out as legacy: modern TUIs position explicitly and draw with Unicode, so wrapping them would be padding, not capability.)

Deferred — genuine scope boundaries (not feasibility)

What remains is deferred on principle, not effort. Each is either a design choice or outside the "small, SBCL-only, terminal-primitives" ethos; none is a decodable capability left on the table:

• Wide-cell skip flag — a design alternative to the spacer-cell model this library already uses for double-width glyphs, not a missing capability. Both render and diff correctly; choosing the other representation would be a rewrite for no user-visible gain.
• Kitty graphics protocol — a second bitmap-output mechanism; format-sixel already covers image output on the widely supported format. Adding kitty graphics would duplicate that surface for terminals that mostly also do sixel.
• Window manipulation (XTWINOPS CSI Ps … t: resize, move, minimize, raise/lower, report position/size) — considered (crossterm exposes a SetSize). Left out because it is window-manager behavior, which Roadmap defers on purpose; the size query it overlaps with is already served by terminal-size (ioctl). Providing the in-terminal rendering escapes is in scope; manipulating the terminal window is not.
• Non-SBCL portability — would require shipping Unicode category/width/grapheme tables the library currently borrows from sb-unicode, against the intentionally-small ethos. Recorded as a standing Roadmap item; see also Compatibility.

Everything marked GAP → DONE, and every item under the second- through fifth-pass lists, was implemented after enumeration and is covered by tests. A later category-by-category re-check against the competitor inventory found no remaining in-scope, non-padding primitive gap: the trivially-derivable candidates (rgb-to-hex, an ansi-cursor-home alias of move 1;1, legacy X10 mouse decoding, hardware tab stops) were rejected as padding, and the only substantive candidate (XTWINOPS) is the window-manipulation boundary above. The enumeration is exhausted down to these principled boundaries.