@tiptap/extension-underline 3.11.0: Underline

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify @tiptap/extension-underline.Underline in pkg:npm/%40tiptap/extension-underline@3.11.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/%40tiptap/extension-underline@3.11.0
Demonstrate these symbols/APIs:
  - @tiptap/extension-underline.Underline

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

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}

{
  "name": "sample",
  "version": "1.0.0",
  "private": true,
  "type": "module",
  "license": "MIT-0",
  "dependencies": {
    "@tiptap/core": "3.11.0",
    "@tiptap/extension-underline": "3.11.0"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify @tiptap/extension-underline.Underline in pkg:npm/%40tiptap/extension-underline@3.11.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/%40tiptap/extension-underline@3.11.0"
  ],
  "symbols": [
    "@tiptap/extension-underline.Underline"
  ]
}

import assert from "node:assert/strict";
import { Node, getSchema } from "@tiptap/core";
import DefaultUnderline, { Underline } from "@tiptap/extension-underline";

// Assertion 1: Underline extension is exported as a mark named underline with default and named export equality
assert.strictEqual(typeof Underline, "object", "Underline must be an object");
assert.strictEqual(Underline.name, "underline", "Underline extension name must be 'underline'");
assert.strictEqual(Underline.type, "mark", "Underline extension type must be 'mark'");
assert.strictEqual(DefaultUnderline, Underline, "Default export must equal named export Underline");
assert.strictEqual(typeof Underline.configure, "function", "Underline must have configure function");
assert.strictEqual(typeof Underline.extend, "function", "Underline must have extend function");

// Assertion 2: Underline extension options can be configured with HTMLAttributes
const defaultOptions = Underline.options;
assert.deepStrictEqual(defaultOptions.HTMLAttributes, {}, "Default HTMLAttributes should be empty object");

const configured = Underline.configure({
  HTMLAttributes: { class: "custom-underline", "data-test": "underline-mark" },
});
assert.strictEqual(configured.name, "underline");
assert.strictEqual(configured.type, "mark");
assert.strictEqual(configured.options.HTMLAttributes.class, "custom-underline");
assert.strictEqual(configured.options.HTMLAttributes["data-test"], "underline-mark");

// Assertion 3: Underline compiles into a ProseMirror schema and generates underline marks
const Doc = Node.create({ name: "doc", topNode: true, content: "block+" });
const Paragraph = Node.create({ name: "paragraph", group: "block", content: "inline*" });
const Text = Node.create({ name: "text", group: "inline" });

const schema = getSchema([Doc, Paragraph, Text, Underline]);
assert.ok(schema.marks.underline, "Schema must include underline mark");
assert.strictEqual(schema.marks.underline.name, "underline");

const mark = schema.marks.underline.create();
assert.strictEqual(mark.type.name, "underline");

const textWithMark = schema.text("underlined text", [mark]);
assert.strictEqual(textWithMark.text, "underlined text");
assert.strictEqual(textWithMark.marks.length, 1);
assert.strictEqual(textWithMark.marks[0].type.name, "underline");

// Assertion 4: Underline mark defines parseHTML rules and renderHTML tag and attributes
const parseRules = Underline.config.parseHTML.call({ options: { HTMLAttributes: {} } });
assert.ok(Array.isArray(parseRules), "parseHTML must return an array of rules");
assert.strictEqual(parseRules[0].tag, "u", "First parse rule tag should be 'u'");

const rendered = Underline.config.renderHTML.call(
  { options: { HTMLAttributes: { class: "rendered-underline" } } },
  { HTMLAttributes: { id: "u-1" } }
);
assert.deepStrictEqual(
  rendered,
  ["u", { class: "rendered-underline", id: "u-1" }, 0],
  "renderHTML must produce expected tag, merged attributes, and hole index"
);

// Assertion 5: Underline defines setUnderline, toggleUnderline, and unsetUnderline commands
assert.strictEqual(typeof Underline.config.addCommands, "function", "addCommands must be defined");
const commands = Underline.config.addCommands.call({
  name: "underline",
  type: Underline.type,
  options: { HTMLAttributes: {} },
});
assert.strictEqual(typeof commands.setUnderline, "function", "setUnderline command must exist");
assert.strictEqual(typeof commands.toggleUnderline, "function", "toggleUnderline command must exist");
assert.strictEqual(typeof commands.unsetUnderline, "function", "unsetUnderline command must exist");

// Assertion 6: Underline defines Mod-u and Mod-U keyboard shortcuts
assert.strictEqual(typeof Underline.config.addKeyboardShortcuts, "function", "addKeyboardShortcuts must be defined");
const shortcuts = Underline.config.addKeyboardShortcuts.call({
  name: "underline",
  type: Underline.type,
  options: { HTMLAttributes: {} },
});
assert.strictEqual(typeof shortcuts["Mod-u"], "function", "Mod-u shortcut must exist");
assert.strictEqual(typeof shortcuts["Mod-U"], "function", "Mod-U shortcut must exist");

console.log("PASS: @tiptap/extension-underline contract verified");