feature: add subscript and superscript extensions, docs and tests

packages/extension-superscript/README.md

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+# @tiptap/extension-superscript
+[![Version](https://img.shields.io/npm/v/@tiptap/extension-superscript.svg?label=version)](https://www.npmjs.com/package/@tiptap/extension-superscript)
+[![Downloads](https://img.shields.io/npm/dm/@tiptap/extension-superscript.svg)](https://npmcharts.com/compare/tiptap?minimal=true)
+[![License](https://img.shields.io/npm/l/@tiptap/extension-superscript.svg)](https://www.npmjs.com/package/@tiptap/extension-superscript)
+[![Sponsor](https://img.shields.io/static/v1?label=Sponsor&message=%E2%9D%A4&logo=GitHub)](https://github.com/sponsors/ueberdosis)
+
+## Introduction
+tiptap is a headless wrapper around [ProseMirror](https://ProseMirror.net) – a toolkit for building rich text WYSIWYG editors, which is already in use at many well-known companies such as *New York Times*, *The Guardian* or *Atlassian*.
+
+## Official Documentation
+Documentation can be found on the [tiptap website](https://tiptap.dev).
+
+## License
+tiptap is open sourced software licensed under the [MIT license](https://github.com/ueberdosis/tiptap/blob/main/LICENSE.md).

packages/extension-superscript/package.json

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+{
+  "name": "@tiptap/extension-superscript",
+  "description": "superscript extension for tiptap",
+  "version": "2.0.0-beta.1",
+  "homepage": "https://tiptap.dev",
+  "keywords": [
+    "tiptap",
+    "tiptap extension"
+  ],
+  "license": "MIT",
+  "funding": {
+    "type": "github",
+    "url": "https://github.com/sponsors/ueberdosis"
+  },
+  "main": "dist/tiptap-extension-superscript.cjs.js",
+  "umd": "dist/tiptap-extension-superscript.umd.js",
+  "module": "dist/tiptap-extension-superscript.esm.js",
+  "types": "dist/packages/extension-superscript/src/index.d.ts",
+  "files": [
+    "src",
+    "dist"
+  ],
+  "peerDependencies": {
+    "@tiptap/core": "^2.0.0-beta.1"
+  }
+}

packages/extension-superscript/src/index.ts

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+import { Superscript } from './superscript'
+
+export * from './superscript'
+
+export default Superscript

packages/extension-superscript/src/superscript.ts

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+import { Command, Mark, mergeAttributes } from '@tiptap/core'
+
+export interface SuperscriptExtensionOptions {
+  HTMLAttributes: Object,
+}
+
+declare module '@tiptap/core' {
+  interface Commands {
+    superscript: {
+      /**
+       * Set a superscript mark
+       */
+      setSuperscript: () => Command,
+      /**
+       * Toggle a superscript mark
+       */
+      toggleSuperscript: () => Command,
+      /**
+       * Unset a superscript mark
+       */
+      unsetSuperscript: () => Command,
+    }
+  }
+}
+
+export const Superscript = Mark.create<SuperscriptExtensionOptions>({
+  name: 'superscript',
+
+  defaultOptions: {
+    HTMLAttributes: {},
+  },
+
+  parseHTML() {
+    return [
+      {
+        tag: 'sup',
+      },
+      {
+        style: 'vertical-align',
+        getAttrs(value) {
+          // Don’t match this rule if the vertical align isn’t super.
+          if (value !== 'super') {
+            return false
+          }
+
+          // If it falls through we’ll match, and this mark will be applied.
+        },
+      },
+    ]
+  },
+
+  renderHTML({ HTMLAttributes }) {
+    return ['sup', mergeAttributes(this.options.HTMLAttributes, HTMLAttributes), 0]
+  },
+
+  addCommands() {
+    return {
+      setSuperscript: () => ({ commands }) => {
+        return commands.setMark('superscript')
+      },
+      toggleSuperscript: () => ({ commands }) => {
+        return commands.toggleMark('superscript')
+      },
+      unsetSuperscript: () => ({ commands }) => {
+        return commands.unsetMark('superscript')
+      },
+    }
+  },
+})