Code block

Overview

link

Web

tanrei-code-block

schedule

SwiftUI

TanreiCodeBlock

radio_button_unchecked

Jetpack Compose

TanreiCodeBlock

radio_button_unchecked

Flutter

TanreiCodeBlock

radio_button_unchecked

React Native

CodeBlock

radio_button_unchecked

Generated from docs/status/status.json, specs/code-block.spec.json

A title, a language label and a copy button; the code is highlighted from its language

// A form's footer: one main action, one way out.
import { Button } from '@tanrei/react';

type FooterProps = { onSave: () => void; busy: boolean };

export function Footer({ onSave, busy }: FooterProps) {
  const retries = 3;
  return (
    <footer className="footer">
      <Button variant="text">Cancel</Button>
      <Button disabled={busy} onClick={onSave}>Save</Button>
    </footer>
  );
}

A code block shows code that people read, compare and copy. A name or a command inside a sentence is Inline code.

The code block highlights code by itself. Give it the code and its language, and it colors the code from tokens: no highlighter to install, no theme and no stylesheet to write. So code follows the scheme, the contrast level and the design system like everything else on the page. Highlighting is color and weight and nothing else: the characters, the lines, what is selected, what is copied and what a screen reader reads are the same with it and without it.

Usage

link

On the web the code stays in your document, as an ordinary <pre><code>. It is there without script: for a reader whose script failed, for search engines, for find-in-page. The element draws the frame around it. Load @tanrei/web/code.css to give a block its fill, corners, padding and face before the element is defined.

SwiftUI, Compose, Flutter and React Native are planned: the names beside each platform at the top of this page are the ones the spec gives them, and nothing ships there yet.

<link rel="stylesheet" href="@tanrei/web/tokens.css" />
<link rel="stylesheet" href="@tanrei/web/code.css" />

<tanrei-code-block
  headline="sizes.js"
  language="js"
  language-label="JavaScript"
  copy
  copy-label="Copy"
  copied-label="Copied"
  copy-failed-label="Could not copy"
>
  <pre><code>const sizes = ['small', 'medium', 'large'];</code></pre>
</tanrei-code-block>

<!-- Numbers, marked lines, a prompt. -->
<tanrei-code-block label="Example" line-numbers start-line="96" highlighted-lines="98, 100-101" highlighted-label="Highlighted">
  <pre><code>…</code></pre>
</tanrei-code-block>

<tanrei-code-block label="Install" prompt="$" copy copy-label="Copy" copied-label="Copied" copy-failed-label="Could not copy">
  <pre><code>npm install @tanrei/web</code></pre>
</tanrei-code-block>

<script type="module">
  import '@tanrei/web';
</script>

import { CodeBlock } from '@tanrei/react';
import '@tanrei/web/code.css';

{/* The element lays the code out in lines, so let it own the code: pass the text. */}
<CodeBlock headline="sizes.js" language="js" languageLabel="JavaScript" code={source} copy copyLabel="Copy" copiedLabel="Copied" copyFailedLabel="Could not copy" />

language is an identifier (tsx, css, sh): it is what the block highlights by, and it is not drawn. The words in the header are language-label. A block built by script sets the code property instead of holding a <pre><code>, and the element writes the <pre><code> itself.

Specs

link

Filled and outlined, medium and small

const sizes = ['small', 'medium', 'large'];

for (const size of sizes) {
  const button = document.createElement('tanrei-button');
  button.setAttribute('size', size);
  document.body.append(button);
}

const sizes = ['small', 'medium', 'large'];

for (const size of sizes) {
  const button = document.createElement('tanrei-button');
  button.setAttribute('size', size);
  document.body.append(button);
}

Line numbers, a highlighted line, and added and removed lines

const sizes = ['small', 'medium', 'large'];

for (const size of sizes) {
  const button = document.createElement('button');
  const button = document.createElement('tanrei-button');
  button.setAttribute('size', size);
  document.body.append(button);
}

A long line scrolls inside the block, or wraps

export const footer = html`<footer class="form-footer"><tanrei-button variant="text" @click=${cancel}>Cancel</tanrei-button><tanrei-button variant="filled" @click=${save}>Save changes</tanrei-button></footer>`;

// The line above is one line: it does not fit and is never cut.

export const footer = html`<footer class="form-footer"><tanrei-button variant="text" @click=${cancel}>Cancel</tanrei-button><tanrei-button variant="filled" @click=${save}>Save changes</tanrei-button></footer>`;

// The line above is one line: it does not fit and is never cut.

A prompt, and a cap on the lines shown

npm install @tanrei/web
npx tanrei studio

01:00 tide high, gauge 1.55 m
02:00 tide falling, gauge 1.90 m
03:00 tide low, gauge 2.25 m
04:00 tide rising, gauge 2.60 m
05:00 tide high, gauge 1.20 m
06:00 tide falling, gauge 1.55 m
07:00 tide low, gauge 1.90 m
08:00 tide rising, gauge 2.25 m

Two looks. filled is a quiet fill, for code on a page. outlined has no fill inside one hairline, for code inside a card or a panel that is already filled.

The body. A line is never broken by default. A line that does not fit scrolls inside the block, and the page never scrolls sideways. wrap breaks lines instead, and a continued row starts under the code, not under the numbers. max-lines caps the height in lines, and the rest scrolls inside the block.

The copy button is always drawn, never only on hover. It never covers code that cannot be moved clear of it: a scrolling body gains that much room at its end, and wrapped rows stop before its column. It copies the code as plain text, without line numbers, the prompt, the signs or the removed lines. A selection made by hand copies exactly the characters selected.

Marked lines are never marked by color alone.

Mark	Bar at the left edge	Band	Sign	Read before the line
Highlighted	yes	yes		highlighted-label
Added	yes	faint green	+	added-label
Removed	yes	faint red	−	removed-label

Line lists are numbers and ranges separated by commas ("3, 7-9"). They count as the numbers the reader sees, from start-line.

Right to left. Code is always left to right: lines, numbers and the start of scrolling are at the left in every layout. Only the frame mirrors, so the title moves to the right and the copy button to the left.

Anatomy

Part	Description
1 container	The block: a quiet fill (filled) or no fill inside one hairline (outlined), with small corners. As wide as its layout gives it.
2 outline · optional	The outlined look's edge: one hairline inside the container.
3 header · optional	A row above the code that holds the title, the language and, where there is one, the copy button. It has no fill and no line of its own: it is the top of the same container.
4 title · optional	What the code is: a file name or a few words. At the start of the header.
5 language · optional	The language label: the language the code is in, in the product's words. At the end of the header, before the copy button.
6 copy-button · optional	A Copy button (its own component) that copies the code: in the header where there is one, at the block's top end corner otherwise.
7 body	The part that holds the lines and scrolls inside the container when they do not fit.
8 code	The code: its lines, each on one line of the code's text style, each run in the color and weight of its syntax role where the code is highlighted.
9 line-number · optional	A line's number, in the gutter at the left of the code. Drawn, not text.
10 mark · optional	A bar at the left edge of a highlighted, an added or a removed line.
11 sign · optional	A plus or a minus in the gutter of an added or a removed line. Drawn, not text.
12 prompt · optional	A prompt drawn before each line of a block of commands. Drawn, not text.

Properties

Property	Type	Default	Description
code	string	""	The code as plain text, lines separated by line breaks. It is what is drawn, what is highlighted and what is copied. Ignored where runs are given: their texts, joined, are the code.
variant	filled | outlined	"filled"	filled: a quiet fill, for code on a page. outlined: no fill inside one hairline, for code inside a container that is already filled (a card, a panel). A design system may add values.
size	small | medium	"medium"	medium sets the code in the code role (13), for a page and a panel. small sets it in the small code role (12) with less padding, for dense interfaces. A design system may add values.
title	string	""	A file name or a few words that say what the code is ("button.tsx", "Response"). Drawn in the header and used as the block's accessible name.
language	string	""	The language the code is written in, as an identifier ("tsx", "css", "swift", "sh"), read without regard to case. It is what the block highlights by (COD-19, COD-27); it is not drawn. Empty, "text" and "plain" mean code that has no syntax; a language the highlighter does not know is drawn plain.
languageLabel	string	""	The language in the product's words ("TypeScript", "Shell"), drawn in the header. A label only: the block does not highlight by it, and draws no label of its own for language.
highlight	boolean	true	True: the block highlights the code by itself where it can (COD-19). False: it never does, whatever language says; runs the product gives are still drawn in their colors.
label	string	""	The block's accessible name where it has no title ("Example", "Request body"), in the product's language. Not drawn. A block that can scroll needs a title or a label.
wrap	boolean	false	False: a line is never broken, and lines that do not fit scroll sideways inside the block. True: a line that does not fit continues on the next row, and nothing scrolls sideways.
lineNumbers	boolean	false	Draws each line's number in a gutter at the left of the code.
startLine	number	1	The number of the first line: an excerpt of a file keeps the file's numbers. A whole number of 1 or more.
highlightedLines	string	""	The lines the text around the block talks about, by number, as numbers and ranges separated by commas ("3, 7-9"). Numbers are the ones lineNumbers would draw (they count from startLine).
addedLines	string	""	The lines a change adds, written as highlightedLines is.
removedLines	string	""	The lines a change takes away, written as highlightedLines is. They are drawn and are left out of what the copy button copies.
highlightedLabel	string	""	What assistive technology reads before a highlighted line ("Highlighted"), in the product's language. Required while highlightedLines names a line.
addedLabel	string	""	What assistive technology reads before an added line ("Added"). Required while addedLines names a line.
removedLabel	string	""	What assistive technology reads before a removed line ("Removed"). Required while removedLines names a line.
prompt	string	""	A prompt ("$", ">") drawn before every line that is not empty, for a block of commands to type. It is not part of the code: it is not selected, not copied and not read.
maxLines	number	null	The most lines shown at once; more than that scroll up and down inside the block. Null shows every line.
copy	boolean	false	Draws a copy button that copies the code.
copyLabel	string	""	The copy button's accessible name ("Copy"), in the product's language. Required while copy is true.
copiedLabel	string	""	What the copy button announces when the code has been copied ("Copied"). Required while copy is true.
copyFailedLabel	string	""	What the copy button announces when the platform refuses the copy ("Could not copy"). Required while copy is true.

Events

Event	Description
copied	The code was copied by the block's copy button; carries the text that was copied.
copyFailed	The platform refused the copy asked for by the block's copy button.

Items

The kinds of item the component repeats. A fixture lists its items in order; each platform names each kind in its own idiom.

run

A piece of the code that is one kind of thing — a comment, a keyword, a string, a function's name — as the block's highlighter found it, or as the product names it where the product gives the runs. The runs' texts, in order, are the code.

Property	Type	Default	Description
text	string	""	The run's characters, exactly as in the code. It may hold line breaks: a run may span lines.
syntax	plain | comment | keyword | string | constant | function | type | tag | property | punctuation	"plain"	What the run is. comment: a comment or a documentation comment. keyword: one of the language's own words (a keyword, a storage or modifier word, an at-rule, an annotation, an operator written as a word). string: text written in the code (a string, a character, a regular expression, the value of a markup attribute). constant: a value that is not text (a number, a boolean or null, a named constant, a unit, a color value, an escape inside a string). function: the name of a function or a method, declared or called. type: the name of a type (a class, a structure, an interface, an enumeration, a built-in type, a namespace). tag: what markup and style sheets address (an element's name, a component's name in markup, a selector). property: a name that belongs to something (a property, a key, a markup attribute, a style declaration's property, a command's option). punctuation: brackets, separators and the delimiters of markup. plain: none of these — variables, parameters, operators written as signs, text between tags. The values are those of the token axis comp.code-block.syntax and plain; a design system may add values to that axis.

Spec	Web	SwiftUI	Jetpack Compose	Flutter	React Native
Item	span	TanreiCodeRun	TanreiCodeRun	TanreiCodeRun	CodeRun
text · Property	textContent	text	text	text	text
syntax · Property	data-syntax	syntax	syntax	syntax	syntax
Notes	A <span data-syntax="keyword"> inside the light-DOM <code>; text outside any such span is plain. Not a custom element. It is what the element's highlighter writes, what highlightToHtml writes where the page is made, and what a product's own highlighter writes — one form, so the stylesheet and the element cannot tell them apart and do not need to.	TanreiCodeRun(_ text: String, _ syntax: TanreiSyntaxRole = .plain), given as runs:; AttributedString ranges carrying a tanreiSyntax attribute are accepted in its place, which is what a highlighter that returns an attributed string gives.	TanreiCodeRun(text, syntax = TanreiSyntaxRole.Plain) in runs; an AnnotatedString whose ranges carry a TanreiSyntaxRole annotation is accepted in its place.	TanreiCodeRun(text, [TanreiSyntaxRole syntax = TanreiSyntaxRole.plain]) in runs:; TanreiCodeBlock.fromSpans takes the TextSpan tree of a highlighter with a function that names each span's role.	An entry of the runs prop: { text: 'const', syntax: 'keyword' }.

States

Behavior

Requirements in EARS form. Every platform implementation is tested against these ids.

ID	Requirement
COD-1	THE code block SHALL draw a container filled with the container color of its variant (comp.code-block.filled.container.color for filled, comp.code-block.outlined.container.color for outlined), with corners comp.code-block.container.shape eased by sys.shape.corner-smoothing and no elevation, as wide as its layout gives it and never wider, and SHALL bring no space outside itself: the layout it sits in spaces it (PRS-15). WHILE variant is outlined it SHALL draw an edge comp.code-block.outline.width wide in comp.code-block.outline.color inside the container's size, following its corners; WHILE variant is filled it SHALL draw no edge.
COD-2	THE code block SHALL set the code in the text style of its size, taken whole (comp.code-block.code.typescale.medium for medium, and so on), in comp.code-block.code.color where a run names no syntax role, every line of the code on one line of that style; it SHALL draw the characters as given — every space kept, a tab advancing to the next multiple of comp.code-block.code.tab-size columns, nothing hyphenated, transformed, translated or spell-checked — and SHALL draw no empty last line for one line break at the end of the code.
COD-3	THE code block SHALL pad the code by the block padding of its size above the first line and below the last (comp.code-block.container.padding-block.medium for medium, and so on) and by the inline padding of its size (comp.code-block.container.padding-inline.medium for medium, and so on) before the start of the lines, or of the gutter where there is one (COD-13), and after the end of the longest line.
COD-4	WHILE wrap is false THE code block SHALL NOT break a line; WHEN a line is wider than the body THE body SHALL scroll sideways inside the container, by pointer, touch, the wheel and the keyboard (COD-7), the page SHALL NOT scroll sideways for it, and the padding after the longest line SHALL scroll with the code, so that its last character can be brought clear of the container's edge. The header and the copy button SHALL NOT scroll with the code. A gesture or a wheel movement up or down over a body that cannot scroll that way SHALL scroll the page.
COD-5	WHILE wrap is true THE code block SHALL continue a line that does not fit on following rows: it breaks first at the spaces of the line and, where a part with no space is wider than the row, between any two characters; a following row SHALL begin at the column where the line's code begins (after the gutter and the prompt), draw no mark of its own and add no character; the body SHALL NOT scroll sideways; and what is selected or copied SHALL hold the line breaks of the code alone.
COD-6	WHILE maxLines is a number and the code has more lines than that THE body SHALL be maxLines lines of the code's text style high plus its paddings and SHALL scroll up and down inside the container; the header and the copy button SHALL NOT scroll with it. WHILE maxLines is null, or the code has no more lines than it, THE code block SHALL be as tall as its lines.
COD-7	WHILE the body can scroll, sideways or up and down, THE body SHALL be one stop in the focus order after the copy button, SHALL scroll by the arrow keys, Page Up, Page Down, Home and End as its platform scrolls any region, and, WHEN it has keyboard focus, SHALL show the focus indicator inside the container's edge, its corners following comp.code-block.container.shape, as sys.behavior.focus-style names (ring or glow), without animation; focus gained by pointer or touch SHALL NOT show it; a platform that cannot draw a choice SHALL fall back to the first value and state that in its README. WHILE the body cannot scroll it SHALL NOT be a stop in the focus order.
COD-8	WHILE title or languageLabel is not empty THE code block SHALL draw a header above the code, in the same container, with no fill and no line of its own: the title at the start, in comp.code-block.title.typescale and comp.code-block.title.color, on one line, laid out as text of its own direction and cut with an ellipsis at the end of that direction when it does not fit; the language label (languageLabel) at the end, before the copy button where there is one, in comp.code-block.language.typescale and comp.code-block.language.color, never cut; its items comp.code-block.header.gap apart. The header's row SHALL begin comp.code-block.copy-button.inset from the container's top edge, be as tall as the copy button where there is one and as one line of the title's text style otherwise, with its items centred on it; the title SHALL begin at the inline padding of COD-3; and the code SHALL begin comp.code-block.header.padding-block-end below the row in place of the block padding of COD-3.
COD-9	WHILE copy is true THE code block SHALL place a Copy button (CPY) — icon-only, of the text variant and the small size, named by copyLabel, with copiedLabel and copyFailedLabel as its two announcements — comp.code-block.copy-button.inset from the container's top edge and from its end edge: at the end of the header where there is one, and over the top end corner of the body otherwise. THE copy button SHALL be drawn whenever the block is, never only under a pointer or on focus; SHALL come before the body in the focus order and in reading order; and SHALL keep its place and size in every form it takes (CPY-7). THE container SHALL be at least as tall as the copy button plus twice that inset.
COD-10	WHILE copy is true and there is no header THE code block SHALL keep code readable beside the button: WHILE wrap is false the padding after the longest line (COD-3, COD-4) SHALL be widened by the button's width and that inset, so that any line's end can be scrolled clear of the button; WHILE wrap is true every row SHALL end before the button's column. THE copy button SHALL stand on a patch of the container's own color where code can pass under it.
COD-11	THE copy button of COD-9 SHALL copy the code as plain text: its lines in order, joined by line breaks, without line numbers, prompts, signs or labels, without the lines removedLines names, and with no line break that wrapping added. WHEN the Copy button emits copied or copyFailed THE code block SHALL emit its own event of that name, copied carrying the text.
COD-12	WHEN a person selects in the body THE code block SHALL select characters of the code alone: line numbers, prompts, signs, bars and the labels of COD-15 and COD-16 SHALL NOT be selectable and SHALL NOT be part of what a copied selection holds; a copied selection SHALL hold the selected characters, removed lines included where they were selected, with the code's own line breaks.
COD-13	WHILE lineNumbers is true THE code block SHALL draw before each line its number, counting from startLine, in the code's text style with digits of one width, in comp.code-block.line-number.color, right-aligned in a column as wide as the widest number drawn; a line that wraps SHALL carry its number on its first row only. The gutter — from the left: the bar's column (COD-15), the numbers, the signs (COD-16) — SHALL stand comp.code-block.line-number.gap from the start of the code, SHALL stay in view on the container's color while the code scrolls sideways under it, and SHALL be kept from assistive technology.
COD-14	THE code block SHALL read highlightedLines, addedLines and removedLines as numbers and ranges separated by commas, each number being a line's number as COD-13 counts it whether or not numbers are drawn; it SHALL ignore a number outside the code and an entry it cannot read, and in debug builds report it. A line named as both added and removed SHALL be drawn removed, and in debug builds reported; a line named as highlighted and as added or removed SHALL be drawn as both.
COD-15	WHILE a line is highlighted THE code block SHALL draw behind all of its rows a band of comp.code-block.line.highlighted.container.color from the container's left edge to its right, and at the container's left edge a bar comp.code-block.line.mark.width wide in comp.code-block.line.highlighted.mark.color as tall as the line; and SHALL expose highlightedLabel to assistive technology before the line's text, without drawing it. The line's code SHALL keep its colors.
COD-16	WHILE a line is added or removed THE code block SHALL draw at the container's left edge a bar comp.code-block.line.mark.width wide, as tall as the line, and in the gutter after the numbers a sign in the code's text style — a plus (+) for an added line, a minus (−) for a removed one — both in comp.code-block.line.added.mark.color for an added line and comp.code-block.line.removed.mark.color for a removed one; and SHALL expose addedLabel or removedLabel before the line's text, without drawing it. THE code block SHALL also draw behind the line, from the container's left edge to its right and under the bar, the sign and the code, a band in comp.code-block.line.added.container.color for an added line and comp.code-block.line.removed.container.color for a removed one, so that a reader scanning the block tells added from removed lines whatever the colors of their code. The line's code SHALL keep its syntax colors, which are held on these bands at the contrast of code text, and SHALL NOT be struck through: the sign and the label say what the line is, never the color alone.
COD-17	WHILE prompt is not empty THE code block SHALL draw the prompt and one space of the code's text style before the first row of every line that is not empty, in comp.code-block.prompt.color, after the gutter; following rows of a wrapped line SHALL begin under the code, not under the prompt; the prompt SHALL be kept from assistive technology and is not code (COD-11, COD-12).
COD-18	THE code block SHALL draw each run in the color of its syntax role — comp.code-block.syntax.color.comment for comment, comp.code-block.syntax.color.keyword for keyword, comp.code-block.syntax.color.string for string, comp.code-block.syntax.color.constant for constant, comp.code-block.syntax.color.function for function, comp.code-block.syntax.color.type for type, comp.code-block.syntax.color.tag for tag, comp.code-block.syntax.color.property for property, comp.code-block.syntax.color.punctuation for punctuation, and comp.code-block.code.color for plain — and with the weight of the code's text style plus the emphasis of its role (comp.code-block.syntax.emphasis.keyword for keyword, and so on; none for plain), whether the block's highlighter found the run (COD-19) or the product gave it (COD-29). A syntax role SHALL change a run's color and weight alone — never its size, family, spacing, slant, decoration or background — so that highlighted code and the same code drawn plain have the same lines, columns and size. A role a design system added to the axis SHALL be drawn from that role's two tokens in the same way.
COD-19	WHILE highlight is true, the product gives no runs (COD-29), language names a language the highlighter knows (COD-27) and the code is no longer than comp.code-block.syntax.max-length characters THE code block SHALL highlight the code by itself: its highlighter reads the code as that language and names the syntax role of every run, and the block draws the runs as COD-18 says. Highlighting SHALL change nothing but colors and weights: the code's characters, its lines, what is selected, what is copied (COD-11, COD-12) and what assistive technology reads (COD-22) are those of the code as given. In every other case THE code block SHALL draw all of the code in comp.code-block.code.color. WHEN a run names a syntax role the active design system does not have THE code block SHALL draw that run as plain, and in debug builds report the unknown role.
COD-20	THE code block SHALL lay out the body left to right in every layout direction (PRS-26): lines begin at the left, the gutter, the bars and the bands' start are at the left, the prompt is at the left of its line, and sideways scrolling starts at the left. WHERE the layout direction is right-to-left THE code block SHALL mirror the frame alone: the title at the right of the header, the language and the copy button at the left, and the copy button of a block without a header at the top left corner; the paddings of COD-10 SHALL then apply at the button's side. A comment written in a right-to-left script SHALL be laid out by the bidirectional algorithm inside its left-to-right line.
COD-21	THE code block SHALL take its layout direction from where it is used — the direction of the nearest ancestor that sets one, and the platform's own where none does — and SHALL have no direction setting of its own; WHEN that direction changes while the code block is shown THE code block SHALL draw itself for the new direction at once, without a motion of its own, keeping its scroll offsets, its selection and its focus.
COD-22	THE code block SHALL expose its code to assistive technology as text in reading order, line after line, with the role of code where the platform has one, inside a group named by title where it is not empty and by label otherwise; the language label SHALL be read as text of the header and language itself SHALL NOT be read; a syntax role SHALL NOT be exposed, and colors arriving or changing (COD-28, COD-30) SHALL NOT be announced; and WHEN code, the runs or a marked line changes THE code block SHALL draw and expose the new content at once, without a motion, SHALL NOT announce the change, and SHALL keep the body's scroll offsets where the content still reaches them.
COD-23	WHERE the platform draws with a person's own forced colors THE code block SHALL draw an edge comp.code-block.outline.width wide in the platform's text color inside its container in every variant; its code in the platform's text color whatever syntax role a run names, every run keeping the weight of its role; line numbers, prompts, signs and bars in that text color; and no band: a highlighted line is then marked by its bar, and an added or a removed line by its bar and its sign.
COD-24	WHILE the text size is enlarged THE code block SHALL grow its lines, its gutter and its header with the text, keeping its paddings and its corners, and the copy button SHALL keep the size and the target of its own spec; at twice the text size in a container 320 wide the body SHALL scroll inside the container (COD-4) or wrap (COD-5), the title SHALL be cut as COD-8 says, and the page SHALL NOT scroll sideways.
COD-25	IF code is empty and no runs are given THE code block SHALL draw nothing, take no space and expose nothing, and in debug builds report that a code block has no code. WHILE copy is true and copyLabel, copiedLabel or copyFailedLabel is empty, WHILE a line is marked and the label of its mark (highlightedLabel, addedLabel, removedLabel) is empty, and WHILE the body can scroll and both title and label are empty THE code block SHALL still draw, and in debug builds report what is missing. WHEN variant or size names a value the active design system does not have THE code block SHALL render with the default value, and in debug builds report the unknown value; a startLine below 1 or not whole SHALL be taken as 1 and a maxLines below 1 as null.
COD-26	THE code block SHALL NOT take a press itself and has no hovered, pressed, selected or disabled state: it draws no state layer and no ripple. What is pressed inside it is its Copy button, which answers a press as its own spec says (CPY-12 to CPY-14).
COD-27	THE code block SHALL read language as an identifier, without regard to case and to space around it, and match it against the names and the other names of the languages its highlighter knows. THE highlighter the code block brings SHALL know these languages: markup (html, xml, svg), css, javascript (js, mjs, cjs, jsx), typescript (ts, tsx), json (jsonc), shell (sh, bash, zsh), swift, kotlin (kt) and dart; a product SHALL be able to add a language, to replace one, and to replace the highlighter whole, once for all the code blocks it draws. WHILE language is empty, "text", "plain" or "plaintext" THE code block SHALL draw the code plain and report nothing; WHILE language names a language the highlighter does not know it SHALL draw the code plain, and in debug builds report the unknown language once for each name. THE code block SHALL NOT guess a language from the code, from title or from languageLabel.
COD-28	THE code block SHALL draw the code at once, plain, without waiting for its highlighter: no part of the highlighter is loaded for a block that will not use it, and a block that waits for it is complete in every other respect. WHEN the runs are ready THE code block SHALL draw every color and weight in one frame, without a motion and without a fade, moving no line and no character, changing the size of nothing, and keeping the body's scroll offsets, the selection and the focus. WHERE the runs are already with the code when the block is first drawn (code highlighted where the page was made) THE code block SHALL draw them in its first frame.
COD-29	WHERE the product gives runs THE code block SHALL take the runs' texts, joined in order, as the code, SHALL draw them as COD-18 says, and SHALL NOT highlight the code itself, whatever language and highlight say: code that was highlighted where the page was made, or by a highlighter the product chose for one block, is drawn as it was given. Code given with the statement that it has been highlighted and has no run with a role SHALL be drawn plain in the same way.
COD-30	WHEN code, language or highlight changes while the block is shown THE code block SHALL draw the new code at once and highlight it again; a result for code that is no longer the code shown SHALL be dropped, never drawn. WHERE its highlighter can answer in the same frame THE code block SHALL draw the new code with its colors in that frame. Otherwise the lines before the first line that changed SHALL keep their colors until the new runs are ready, and the lines from there on SHALL be drawn plain until then, so that code that grows at its end does not lose and regain its colors with every piece.
COD-31	WHILE the code is longer than comp.code-block.syntax.max-length characters THE code block SHALL draw all of it plain — never a part of it highlighted — and in debug builds report that the code is too long to highlight. Runs the product gives are drawn whatever their length.
COD-32	IF the highlighter cannot be loaded, fails while it reads the code, or answers with runs whose texts do not join to the code exactly THEN THE code block SHALL draw the code plain, SHALL keep everything else it draws and does — the header, the copy button, the lines, the marks, scrolling — and in debug builds report what failed. A failure in one block SHALL NOT change another block.
COD-33	WHILE addedLines or removedLines names a line THE code block SHALL highlight the code as the two texts it holds: the lines that are not removed, in order, are read as one text — the code as it is after the change, which is what is copied (COD-11) — and color the lines that are not removed; the lines that are not added, in order, are read as another — the code as it was before — and color the removed lines. A highlighted line and an added or a removed line SHALL keep the colors of their runs over the band and beside the bar and the sign (COD-15, COD-16).
COD-34	WHERE the platform has ARIA attributes (the web), WHEN the product sets an aria- attribute on the host, by the attribute or by the ARIA property that reflects it, THE code block SHALL move it to the data-aria- attribute of the same name, so that the host is no second node with its name, description or state, and SHALL expose it on its body, which SHALL be a group WHILE it has a name: its title or label, or one given so — an id reference by the elements it names in the host's tree or a tree around it, a description after its own. WHILE the title or label is not empty it is the body's name, over a name given so; a name given so SHALL count as the body's name for the report of COD-25. WHEN the product removes the aria- attribute or its data-aria- twin, or sets the ARIA property that reflects it (ariaLabel, ariaDescribedByElements…) to null, THE code block SHALL take it off that element.

Platform name mapping

Parity does not mean identical APIs. Each platform uses its own idiom for the same contract.

Spec	Web	SwiftUI	Jetpack Compose	Flutter	React Native
Component	tanrei-code-block	TanreiCodeBlock	TanreiCodeBlock	TanreiCodeBlock	CodeBlock
code · Property	code	code	code	code	code
variant · Property	variant	variant	variant	variant	variant
size · Property	size	size	size	size	size
title · Property	headline	title	title	title	title
language · Property	language	language	language	language	language
languageLabel · Property	languageLabel	languageLabel	languageLabel	languageLabel	languageLabel
highlight · Property	highlight	highlightsSyntax	highlightSyntax	highlightSyntax	highlight
label · Property	label	label	label	label	label
wrap · Property	wrap	wrapsLines	softWrap	softWrap	wrap
lineNumbers · Property	lineNumbers	showsLineNumbers	showLineNumbers	showLineNumbers	showLineNumbers
startLine · Property	startLine	startLine	startLine	startLine	startLine
highlightedLines · Property	highlightedLines	highlightedLines	highlightedLines	highlightedLines	highlightedLines
addedLines · Property	addedLines	addedLines	addedLines	addedLines	addedLines
removedLines · Property	removedLines	removedLines	removedLines	removedLines	removedLines
highlightedLabel · Property	highlightedLabel	highlightedLabel	highlightedLabel	highlightedLabel	highlightedLabel
addedLabel · Property	addedLabel	addedLabel	addedLabel	addedLabel	addedLabel
removedLabel · Property	removedLabel	removedLabel	removedLabel	removedLabel	removedLabel
prompt · Property	prompt	prompt	prompt	prompt	prompt
maxLines · Property	maxLines	lineLimit	maxLines	maxLines	maxLines
copy · Property	copy	showsCopyButton	showCopyButton	showCopyButton	copy
copyLabel · Property	copyLabel	copyLabel	copyLabel	copyLabel	copyLabel
copiedLabel · Property	copiedLabel	copiedLabel	copiedLabel	copiedLabel	copiedLabel
copyFailedLabel · Property	copyFailedLabel	copyFailedLabel	copyFailedLabel	copyFailedLabel	copyFailedLabel
copied · Event	copied	onCopied	onCopied	onCopied	onCopied
copyFailed · Event	copyfailed	onCopyFailed	onCopyFailed	onCopyFailed	onCopyFailed
Notes	<tanrei-code-block headline="sizes.js" copy copy-label="Copy" …><pre><code>…</code></pre></tanrei-code-block>: the code stays in the light DOM as an ordinary <pre><code>, so it is in the document without script — for a reader whose script failed, for search engines and crawlers, for find-in-page and for the browser's own copy — and the element decorates it. The shadow root draws the header, the copy button (<tanrei-copy-button>), the focus ring and the scrolling body, and slots the <pre>; the code is read from the slotted <code>'s text, and the code attribute is for a block built by script (the element then writes the <pre><code> itself). Runs are <span data-syntax="…"> in that <code> (COD-18); the stylesheet colors them with ::slotted being unable to reach them, so the rules live in the optional light-DOM stylesheet @tanrei/web/code.css, scoped to tanrei-code-block, which also gives a not-yet-upgraded or script-less block its fill, corners, padding, face and overflow-x: auto through tanrei-code-block:not(:defined) and a bare .tanrei-prose pre (the pre rules are there, not in prose.css). Lines: the element needs one box per line for numbers, marks, the prompt and wrapping; it uses [data-line] children of the <code> where the highlighter emitted them and otherwise wraps each line in a <span data-line> on upgrade, moving nodes and splitting text nodes and spans at line breaks without adding or removing a character, so textContent is unchanged. Line numbers, signs and the prompt are ::before content of the line (counter(), with an empty alternative text so they are not read), user-select: none; the gutter is position: sticky; left: 0 on the container's color. highlighted-lines, added-lines and removed-lines are attributes; the element sets data-highlighted, data-added or data-removed on the lines and puts each label in a visually hidden, unselectable prefix referenced from the line. The body is the scroll container with tabindex="0", role="group" and aria-label only while it overflows (a ResizeObserver decides); dir="ltr" on the body, and the host mirrors the header by :dir() (COD-20). tab-size from the token. COD-11 writes through the copy button with a text built from the lines, not from innerText. **Highlighting.** highlight is a boolean that is true by default, so its attribute is written to turn it off: highlight="false" (the property takes a boolean). The highlighter is the module @tanrei/web/highlight: no dependency, no DOM, the same file in a browser and in Node. It exports highlight(code, language) (the runs, or null for a language it does not know), highlightToHtml(code, language, { lines }) (the inner HTML of the <code>: escaped text, <span data-syntax> runs and, with lines, one <span data-line> per line), registerLanguage(names, grammar) (a grammar, or a function that imports one), setHighlighter(fn) (replace it whole; null turns automatic highlighting off for the page), languages() and foldScope(scope) (the table that folds a dotted scope name into a syntax role, for a product that brings a highlighter of dotted scope names). The element does not import the module: a block that needs it (COD-19) imports it with import() the first time, and each grammar is a chunk of its own imported the first time its language is asked for, so a page whose code was highlighted where it was made, or that shows no code, loads none of it. Budget, held by a test of the built files: the core of the module at most 3 kB and each grammar at most 3 kB, compressed; tsx and jsx are the typescript and javascript grammars with markup switched on, not grammars of their own. A grammar is data — named states, each an ordered list of rules (a pattern, the role of what it matches, and the state to enter or leave) — read by one small interpreter; patterns are sticky regular expressions without nested quantifiers, so the time to read a text grows with its length and no text can stall the page. The highlighter answers in the same task once its grammar is loaded, which is what lets COD-30 draw new code with its colors in one frame; the first answer for a language waits for the import and the block is plain until then (COD-28). **Code highlighted where the page is made is first-class**: <code data-syntax-of="tsx"> holding <span data-syntax> runs, written by highlightToHtml in a build, a server or a Markdown plugin, is the product's runs (COD-29) — the element reads the attribute or any [data-syntax] it did not write itself and never highlights that code again, so the first paint has its colors and nothing is imported. The element writes its own runs as spans into the same light-DOM <code>, splitting at line boundaries, in one synchronous pass that replaces the children of each changed [data-line] and touches no other line (COD-30); it marks the runs it wrote so that it can tell them from the product's. Spans, not the CSS Custom Highlight API: a highlight registered by script cannot be in the HTML a server sends, and ::highlight() may set a color but not a weight, which is how keywords are told (COD-18); for assistive technology the two are the same, since neither adds a role. A framework that owns the children of the <code> (it renders them from state) should pass code as a property and let the element write the <pre><code>, or give the runs itself. comp.code-block.syntax.max-length is read from the generated tokens module, not from CSS. The colors are rules of @tanrei/web/code.css, one per value of the syntax axis, generated from the tokens so that a role a layer adds gets its rule.	TanreiCodeBlock(code:, runs:, variant:, size:, title:, …). The body is a ScrollView (horizontal, and vertical under lineLimit) holding a Text per line with textSelection(.enabled); the gutter is a separate, non-selectable column pinned beside it. The body's layout direction is forced to left-to-right in the environment (COD-20). The marks' labels are the line's accessibility label prefix. Automatic highlighting is not built on this platform yet; as specified, it is the same grammars, which are data, read by an interpreter written in Swift over NSRegularExpression, behind TanreiCodeHighlighter — a protocol the product may implement to bring its own — set once in the environment; highlightsSyntax: Bool = true. Until then this platform draws runs the product gives and code without runs plain, and says so in its README.	TanreiCodeBlock(code, runs, variant, size, title, …). The body is a SelectionContainer over a BasicText in horizontalScroll (and verticalScroll under maxLines), inside CompositionLocalProvider(LocalLayoutDirection provides Ltr) (COD-20); the gutter is drawn beside it and cleared from semantics. The body is focusable only while its scroll state reports a range. Automatic highlighting is not built on this platform yet; as specified, it is the same grammars read by an interpreter written in Kotlin over kotlin.text.Regex, behind a TanreiCodeHighlighter interface provided by a CompositionLocal; the runs are computed off the main thread in a produceState keyed by the code and the language, which is this platform's form of COD-30's cancellation. Until then this platform draws runs the product gives and code without runs plain, and says so in its README.	TanreiCodeBlock(code: …, runs: …, variant:, size:, title:, …). The body is a SelectableText.rich in a horizontal SingleChildScrollView with a Scrollbar, under Directionality(textDirection: TextDirection.ltr) (COD-20); the gutter is a column beside it wrapped in ExcludeSemantics. A Focus node on the body exists only while the scroll position has an extent. Automatic highlighting is not built on this platform yet; as specified, it is the same grammars read by an interpreter written in Dart over RegExp, behind a TanreiCodeHighlighter the theme carries; long code is read in an isolate. Until then this platform draws runs the product gives and code without runs plain, and says so in its README.	<CodeBlock code="…" runs={…} title="sizes.js" />. The body is a horizontal ScrollView holding <Text selectable> lines with writingDirection: 'ltr'; the gutter is a sibling column with importantForAccessibility="no-hide-descendants" and accessibilityElementsHidden. Copying goes through the Copy button (see its note on the clipboard module). Follows the app's direction where an ancestor's is not known. Automatic highlighting is not built on this platform yet; as specified, it is the highlighter module of the web package, which has no DOM, imported as it is; a highlighter prop of the provider replaces it. Until then this platform draws runs the product gives and code without runs plain, and says so in its README.

Tokens

Token	Aliases	Resolved (light)
--tanrei-comp-code-block-code-color	sys.color.on-surface	#1b1b1b
--tanrei-comp-code-block-code-tab-size	—	2
--tanrei-comp-code-block-container-padding-block-medium	sys.space.space150	12px
--tanrei-comp-code-block-container-padding-block-small	sys.space.space100	8px
--tanrei-comp-code-block-container-padding-inline-medium	sys.space.space200	16px
--tanrei-comp-code-block-container-padding-inline-small	sys.space.space150	12px
--tanrei-comp-code-block-container-shape	sys.shape.corner.small	6px
--tanrei-comp-code-block-copy-button-inset	sys.space.space75	6px
--tanrei-comp-code-block-filled-container-color	sys.color.surface-container	#f6f6f6
--tanrei-comp-code-block-header-gap	sys.space.space100	8px
--tanrei-comp-code-block-header-padding-block-end	sys.space.space50	4px
--tanrei-comp-code-block-language-color	sys.color.on-surface-variant	#4b4b4b
--tanrei-comp-code-block-line-number-color	sys.color.on-surface-variant	#4b4b4b
--tanrei-comp-code-block-line-number-gap	sys.space.space200	16px
--tanrei-comp-code-block-line-added-container-color	sys.color.success-container	#e2f6df
--tanrei-comp-code-block-line-added-mark-color	sys.color.success	#077b32
--tanrei-comp-code-block-line-highlighted-container-color	sys.color.surface-container-highest	#eeeeee
--tanrei-comp-code-block-line-highlighted-mark-color	sys.color.primary	#1b1b1b
--tanrei-comp-code-block-line-mark-width	sys.border.thick	2px
--tanrei-comp-code-block-line-removed-container-color	sys.color.error-container	#ffedeb
--tanrei-comp-code-block-line-removed-mark-color	sys.color.error	#cd262f
--tanrei-comp-code-block-outline-color	sys.color.outline-variant	#000000 · 8%
--tanrei-comp-code-block-outline-width	sys.border.hairline	1px
--tanrei-comp-code-block-outlined-container-color	—	#000000 · 0%
--tanrei-comp-code-block-prompt-color	sys.color.on-surface-variant	#4b4b4b
--tanrei-comp-code-block-syntax-color-comment	sys.color.on-surface-variant	#4b4b4b
--tanrei-comp-code-block-syntax-color-constant	sys.color.on-surface	#944b00
--tanrei-comp-code-block-syntax-color-function	sys.color.on-surface	#005bbe
--tanrei-comp-code-block-syntax-color-keyword	sys.color.on-surface	#833cb3
--tanrei-comp-code-block-syntax-color-property	sys.color.on-surface	#0052ac
--tanrei-comp-code-block-syntax-color-punctuation	sys.color.on-surface-variant	#4b4b4b
--tanrei-comp-code-block-syntax-color-string	sys.color.on-surface	#206c24
--tanrei-comp-code-block-syntax-color-tag	sys.color.on-surface	#b02c34
--tanrei-comp-code-block-syntax-color-type	sys.color.on-surface	#00696c
--tanrei-comp-code-block-syntax-emphasis-comment	—	0
--tanrei-comp-code-block-syntax-emphasis-constant	—	0
--tanrei-comp-code-block-syntax-emphasis-function	—	0
--tanrei-comp-code-block-syntax-emphasis-keyword	sys.typescale.emphasis.body	100
--tanrei-comp-code-block-syntax-emphasis-property	—	0
--tanrei-comp-code-block-syntax-emphasis-punctuation	—	0
--tanrei-comp-code-block-syntax-emphasis-string	—	0
--tanrei-comp-code-block-syntax-emphasis-tag	—	0
--tanrei-comp-code-block-syntax-emphasis-type	—	0
--tanrei-comp-code-block-syntax-max-length	—	50000
--tanrei-comp-code-block-title-color	sys.color.on-surface	#1b1b1b
--tanrei-comp-code-block-code-typescale-medium	sys.typescale.code	400 13px/1.5385
--tanrei-comp-code-block-code-typescale-small	sys.typescale.code-small	400 12px/1.3333
--tanrei-comp-code-block-language-typescale	sys.typescale.label-small	500 12px/1.3333
--tanrei-comp-code-block-title-typescale	sys.typescale.label-small	500 12px/1.3333

Fixtures

Canonical renderings. Every platform snapshots each fixture under the same id so the results can be compared.

variant: filled (43)

plain

code: <tanrei-button variant="filled">Save</ta… label: Example

small

code: const sizes = ['small', 'medium', 'large… size: small label: Example

titled

code: const sizes = ['small', 'medium', 'large… title: sizes.js

titled-language-copy

code: const sizes = ['small', 'medium', 'large… title: sizes.js languageLabel: JavaScript copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy

language-only

code: <tanrei-button variant="filled">Save</ta… languageLabel: HTML label: Example

copy

code: const sizes = ['small', 'medium', 'large… label: Example copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy

one-line-copy

code: npm install @tanrei/web label: Install copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy

syntax

title: Footer.tsx languageLabel: TSX copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy items: 87

syntax-small

size: small label: A layer file items: 38

line-numbers

code: const sizes = ['small', 'medium', 'large… label: Example lineNumbers: true

line-numbers-start

code: const sizes = ['small', 'medium', 'large… title: sizes.js lineNumbers: true startLine: 96

highlighted-lines

code: const sizes = ['small', 'medium', 'large… label: Example lineNumbers: true highlightedLines: 1, 4-5 highlightedLabel: Highlighted

diff

code: const sizes = ['small', 'medium', 'large… title: sizes.js lineNumbers: true addedLines: 5-6 removedLines: 4 addedLabel: Added removedLabel: Removed copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy

diff-without-numbers

code: <tanrei-button variant="filled">Save</ta… label: Example addedLines: 2 removedLines: 1 addedLabel: Added removedLabel: Removed

syntax-marked

title: Footer.tsx lineNumbers: true highlightedLines: 5 addedLines: 9 highlightedLabel: Highlighted addedLabel: Added copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy items: 87

long-lines

code: export const footer = html`<footer class… label: Example

long-lines-copy

code: export const footer = html`<footer class… label: Example copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy

long-lines-wrapped

code: export const footer = html`<footer class… label: Example wrap: true

long-lines-wrapped-numbered-copy

code: export const footer = html`<footer class… label: Example wrap: true lineNumbers: true highlightedLines: 1 highlightedLabel: Highlighted copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy

max-lines

code: 01:00 tide high, gauge 1.55 m 02:00 tide… title: tide.log lineNumbers: true maxLines: 5 copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy

terminal

code: npm install @tanrei/web npx tanrei studi… languageLabel: Shell prompt: $ copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy

terminal-one-line

code: flutter pub add tanrei label: Install prompt: $ copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy

tabs

code: build: node scripts/build.js test: bui… title: Makefile

japanese-comment

label: 例 items: 8

rtl

code: const sizes = ['small', 'medium', 'large… title: مثال languageLabel: JavaScript lineNumbers: true highlightedLines: 3 highlightedLabel: مميز copy: true copyLabel: نسخ copiedLabel: تم النسخ copyFailedLabel: تعذر النسخ direction: rtl

rtl-copy-without-header

code: export const footer = html`<footer class… label: مثال copy: true copyLabel: نسخ copiedLabel: تم النسخ copyFailedLabel: تعذر النسخ direction: rtl

rtl-ltr-title

code: <tanrei-button variant="filled">Save</ta… title: packages/web/src/components/button/butto… copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy direction: rtl

auto-tsx

code: // A form's footer: one main action, one… title: Footer.tsx language: tsx languageLabel: TSX copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy

auto-html

code: <!-- One main action, one way out --> <f… language: html label: Example

auto-css

code: /* The footer of a form */ @media (min-w… language: css label: Example

auto-javascript

code: const sizes = ['small', 'medium', 'large… language: js label: Example

auto-json

code: { "name": "acme", "extends": "tanrei… language: json label: Example

auto-shell

code: # Install and build pnpm add @tanrei/web… language: sh label: Example prompt: $

auto-swift

code: import SwiftUI /// A form's footer. str… language: swift label: Example

auto-kotlin

code: @Composable fun Footer(busy: Boolean, on… language: kotlin label: Example

auto-dart

code: class Footer extends StatelessWidget {… language: dart label: Example

auto-small

code: { "name": "acme", "extends": "tanrei… size: small language: json label: Example

auto-highlighted-lines

code: const sizes = ['small', 'medium', 'large… language: js label: Example lineNumbers: true highlightedLines: 4-5 highlightedLabel: Highlighted

auto-marked

code: const sizes = ['small', 'medium', 'large… language: js label: Example lineNumbers: true addedLines: 3 removedLines: 2 addedLabel: Added removedLabel: Removed copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy

auto-japanese-comment

code: // 保存ボタンは 1 画面に 1 つだけ置く。 const label = '… language: js label: 例

auto-off

code: // A form's footer: one main action, one… language: tsx highlight: false label: Example

auto-text

code: Tanrei 0.1.0 5 platforms, 36 component… language: text label: Example

auto-unknown-language

code: IDENTIFICATION DIVISION. PROGRAM-ID. HEL… language: cobol label: Example

variant: outlined (5)

outlined

code: <tanrei-button variant="filled">Save</ta… variant: outlined label: Example

small-outlined-titled

code: const sizes = ['small', 'medium', 'large… variant: outlined size: small title: sizes.js languageLabel: JavaScript copy: true copyLabel: Copy copiedLabel: Copied copyFailedLabel: Could not copy

syntax-outlined

variant: outlined label: A layer file items: 38

highlighted-outlined

code: const sizes = ['small', 'medium', 'large… variant: outlined label: Example highlightedLines: 3 highlightedLabel: Highlighted

auto-outlined

code: // A form's footer: one main action, one… variant: outlined language: tsx label: Example

Generated from specs/code-block.spec.json, tokens/comp/code-block.tokens.json, design/tokens/

Highlighting

link

Color comes from one of three sources, in this order.

1. Runs you give. Code highlighted where the page was made, or by a highlighter you chose. They are drawn as given, and the block never highlights that code again, whatever language and highlight say.
2. The block’s own highlighter, when highlight is true, language names a language it knows, and the code is no longer than comp.code-block.syntax.max-length (50,000 characters).
3. Plain, in every other case.

The code is drawn at once, plain. Its colors arrive a moment later, in one frame, and move nothing. Code that changes is read again, and code that grows at its end keeps the colors it has.

language	What happens
html, xml, svg, css, javascript (js, mjs, cjs, jsx), typescript (ts, tsx), json (jsonc), shell (sh, bash, zsh), swift, kotlin (kt), dart	Highlighted. Case does not matter.
empty, text, plain, plaintext	Plain. Nothing is reported.
anything else	Plain. A debug build reports the unknown language once.

The block never guesses a language, not from the code, the headline or the language-label. Short code is ambiguous, and a wrong guess colors code wrongly.

Turning it off. highlight="false" turns the block’s own highlighter off for one block. Runs you give are still drawn.

A limit. Code longer than comp.code-block.syntax.max-length is drawn plain, all of it, never half highlighted. A design system can change the value.

With added and removed lines, the block reads the code as the two texts it holds: the code after the change colors the lines that are not removed, and the code before it colors the removed lines. A removed line that opens a string cannot miscolor what follows.

Failures are quiet. A highlighter that cannot be loaded, that throws, or whose runs do not join to the code exactly leaves the code plain. The header, the copy button, the lines and the marks keep working.

The grammars are small on purpose. They are meant for showing code, not for editing it. Where a language is hard they can put a run in the wrong color, but they never drop a character.

Highlighting where the page is made

link

A site that builds its pages can highlight in the build. The colors are then in the first paint, and the browser loads no highlighter. highlightToHtml is the same function the element uses, and it runs in Node.

import { highlightToHtml } from '@tanrei/web/highlight';

const html = await highlightToHtml(source, 'tsx');
// <tanrei-code-block language="tsx"><pre><code data-syntax-of="tsx">${html}</code></pre></tanrei-code-block>

data-syntax-of on the <code> says that the code has been highlighted. The element draws it as given and imports nothing.

Your own highlighter

link

@tanrei/web/highlight is a module of its own with no dependency. The element imports it the first time a block needs it, and each language’s grammar the first time that language is asked for.

Export	What it does
highlight(code, language)	The runs, or null for a language it does not know. A promise the first time a language is used, a value after.
highlightToHtml(code, language, { lines })	The inner HTML of the <code>. With lines, one <span data-line> per line.
registerLanguage(names, grammar)	Adds a language or replaces one. A grammar is data: named states, each a list of rules with a pattern, a role and the state to enter or leave. It may be a function that imports the grammar.
loadLanguage(language)	Loads a grammar ahead of the first code in it.
setHighlighter(fn)	Replaces the highlighter whole. null turns automatic highlighting off for the page.
languages()	Every name a language is known by.
foldScope(scopes, text)	The role for a dotted scope name, by the table below.
tokenize(grammar, code), checkGrammar(grammar)	For testing a grammar you write.

A product that already has a highlighter it trusts can also set TanreiCodeBlock.highlighter to a function (code, language, signal) => runs. The block then asks that function, and Tanrei’s module is never loaded.

Syntax roles

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Role (data-syntax)	What it is	In the default system
comment	A comment, a documentation comment	Quieter than the code
keyword	One of the language’s own words: a keyword, a modifier, an at-rule, an annotation, an operator written as a word	Purple, one weight step heavier
string	Text written in the code: a string, a character, a regular expression, the value of a markup attribute	Green
constant	A value that is not text: a number, a boolean, null, a named constant, a unit, a color value, an escape	Orange
function	The name of a function or a method, declared or called	Blue
type	The name of a type: a class, a structure, an interface, a built-in type, a namespace	Blue-green
tag	What markup and style sheets address: an element’s name, a component’s name in markup, a selector	Red
property	A name that belongs to something: a property, a key, a markup attribute, a style property, a command’s option	Blue, a tone nearer the code’s color
punctuation	Brackets, separators, the delimiters of markup	Quieter than the code
plain (no span)	Anything else: variables, parameters, operators written as signs, text between tags	The code’s color

Each role has two tokens: a color (comp.code-block.syntax.color.*) and a weight step (comp.code-block.syntax.emphasis.*). The roles are a token axis, so a design system can add one. The default system’s green and red come from palettes that are syntax’s own, close in hue to the success and error colors. An added or a removed line is told by its bar, its sign and its label, never by color alone. A role changes color and weight only, so highlighted and plain code have the same lines and columns.

A run is a <span data-syntax="…"> inside the <code>. Text outside a span is plain.

Runs you give are drawn as given

{
  "name": "acme",
  "dials": { "size.unit": 4 },
  "compact": false
}

Folding a highlighter’s scopes into the roles

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Some highlighters name what they find with dotted scope names from one shared vocabulary. foldScope folds them into the roles, so that your highlighter and Tanrei’s give the same colors. A token’s scopes are tried from the most specific outward. Within one scope the first matching row wins. A scope that matches no row is passed over, and a token that matches nothing is plain.

#	Scope begins with	Role
1	comment, punctuation.definition.comment	comment
2	constant.character.escape, constant.numeric, constant.language, constant.other, keyword.other.unit, support.constant, variable.other.constant, variable.other.enummember	constant
3	string, punctuation.definition.string, markup.inline.raw, markup.raw	string
4	entity.name.tag, support.class.component, meta.selector, and in style sheets entity.other.attribute-name	tag
5	entity.other.attribute-name, support.type.property-name, meta.property-name, meta.object-literal.key, variable.other.property, variable.other.object.property, support.type.vendored.property-name, variable.parameter.option	property
6	entity.name.function, support.function, variable.function, meta.function-call.generic	function
7	entity.name.type, entity.name.class, entity.name.namespace, entity.other.inherited-class, support.type, support.class, storage.type.primitive, storage.type.built-in, keyword.type	type
8	keyword.operator whose text is made of letters (new, typeof, in)	keyword
9	keyword.operator otherwise	plain
10	keyword, storage, variable.language, meta.decorator, punctuation.decorator, entity.name.function.decorator, markup.heading	keyword
11	punctuation, meta.brace, meta.delimiter	punctuation
12	variable, meta, source, text, markup, invalid	plain

• A string’s quotes are part of the string. An escape inside a string is a constant.
• JSON keys are properties, and their values strings and constants.
• A decorator’s name is a keyword.
• invalid is plain. A code display does not judge code.
• Added and removed are properties of a line (added-lines, removed-lines), not of a run.

What the web draws differently

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• The element gives each line a box by wrapping it in <span data-line>. It moves your nodes and splits text and runs at line breaks, and adds no character to the code. A framework that owns the children of the <code> should pass code instead, or render [data-line] itself.
• A marked line’s label is a hidden <span> before the line’s code. It is part of the <code>’s textContent, and is left out of what is copied.
• The outlined look is drawn on whatever it is placed on. Where that is not the surface color, name it in --tanrei-code-block-ground, so the line numbers and the copy button can stand on it while code scrolls under them.
• Before the element is defined, code.css draws the fill, the corners, the padding and the runs’ colors. The header, the copy button, the numbers and the marks need the element.
• highlight is true by default, so its attribute is written to turn it off: highlight="false". The property takes a boolean.
• The element writes its own runs as spans into your <code>, one line at a time, and marks them as its own. A framework that owns the children of the <code> should pass code and let the element write them.
• The limit is read from the custom property --tanrei-comp-code-block-syntax-max-length, as the cascade gives it to the block.
• A page that uses the single-file bundle has the highlighter inside it. A page that imports @tanrei/web as modules loads it on demand.

Guidelines

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Do

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• Give a block that can scroll a headline or a label. The scrolling body is a focus stop and needs a name.
• Use outlined inside a card or a panel, and filled on a page and on a colored container.
• Use a prompt for a block of commands to type. The prompt is not copied.
• Give every block its language. Use language="text" for text that has no syntax.
• Put several files or languages in Tabs that each hold a code block.

Don’t

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• Don’t use a code block for a name in a sentence. Use Inline code.
• Don’t rely on syntax colors to say something. The same code drawn plain must say the same thing.
• Don’t mix commands and their output under one prompt. Every line that is not empty gets the prompt. Use two blocks.

Accessibility

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Role

group

Labeling

The block is a group named by title, or by label where it has no title; inside it the code is text with the role of code where the platform has one. The copy button is named by copyLabel. Line numbers, prompts, signs and bars are hidden; a marked line is preceded by its label in words (highlightedLabel, addedLabel, removedLabel).

Minimum target

The hit area meets the minimum target size even when the visual size is smaller. minimum 32px · pointer 44px · spacing 8px · touch 48px

Keyboard

Keys	Action
Tab	Moves focus to the copy button where there is one, then to the body while it can scroll. A block that neither scrolls nor copies is not a stop.
Arrow keys, Page Up, Page Down, Home, End	Scroll the focused body, as the platform scrolls any region.
Enter / Space	On the copy button: copies the code (CPY-2).

Notes

• The only target is the copy button, whose hit area meets the minimum target by its own spec (CPY-1, BTN-5) though it is drawn 32 high. The body is scrolled, not pressed.
• A body that scrolls must be reachable by keyboard (WCAG 2.1.1) and so is a focus stop with a visible focus indicator (COD-7); one that does not scroll is not, so a page of short examples adds no stops. A group, not a landmark: a page may hold hundreds of blocks.
• Reflow (WCAG 1.4.10): code is two-dimensional content, so sideways scrolling inside the block is allowed, and the page itself never scrolls sideways (COD-4, COD-24). wrap is for a product that prefers no sideways scrolling at all.
• A marked line is never marked by color alone (WCAG 1.4.1): a highlighted line has a bar and a band and its label; an added or a removed line has a bar, a plus or a minus and its label (COD-15, COD-16). Syntax colors carry no meaning a reader needs: the same code drawn plain says the same thing, a role is never exposed (COD-22), and keywords are also told by weight. With a red-green color vision deficiency some of the default system's six hues draw together — the green of a string and the red of a tag's name first — beside the neutral tones and the keyword's weight; nothing is lost but a distinction between kinds of words.
• Contrast: the code, the line numbers, the prompt and the signs are roles the token invariants hold at 4.5:1 on every surface (7:1 in the high-contrast schemes). Every syntax color is held by the build at the same ratios against the block's fill, against the band of a highlighted line and against every surface role, which is what an outlined block may stand on, in each system. The bars are primary, success and error, held at the same ratios, above the 3:1 a mark needs. The outlined look's edge is decorative.
• An outlined block is read on whatever it is placed on. On a surface that is correct. On a colored container (a callout) the syntax colors are not paired with that container: use filled there, which brings its own surface.
• The copy button is always drawn (COD-9): one that appears only under a pointer cannot be found by touch, and one that appears on focus moves under a keyboard user. Its confirmation is announced by the Copy button's own live region (CPY-5).
• Highlighting adds nothing for assistive technology and takes nothing away: the code is the same text before and after the colors arrive, no live region speaks of them, and the body's scroll position, the selection and the focus are kept (COD-28). Colors arrive in one frame, without a motion, so nothing flashes more than once.
• Screen readers read code as text, symbol by symbol as the person's settings say. The code block adds no line numbers or roles to that reading; the marks' labels are the only words it adds.
• Code is not translated and not spell-checked (COD-2); comments in it are the author's language and are read with the page's voice unless the product marks their language.

Generated from specs/code-block.spec.json, tokens/sys/measure.tokens.json

What the component handles

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• The code is the code element inside a group named by headline, or by label.
• A body that can scroll is one stop in the focus order, after the copy button, and scrolls with the arrow keys. A body that fits is not a stop, so a page of short examples adds none.
• Line numbers, signs, bars and the prompt are hidden from assistive technology. A marked line is preceded by its label in words.
• The page never scrolls sideways for a code block, at 320 wide and at twice the text size.
• In forced colors every look gains an edge, all code is the text color, and bars and signs stay.
• Highlighting adds nothing for assistive technology. No role is exposed, and colors that arrive are not announced. The selection, the focus and the scroll position are kept.
• With a red-green color vision deficiency some of the six hues draw together, the green of a string and the red of a tag’s name first. Keywords are also told by weight.

What you need to do

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• Provide copy-label, copied-label and copy-failed-label with copy, and the label of each mark you use, in your product’s language.
• Say in the text around the block what a highlighted line shows. The label only says that it is highlighted.