Add latest changes from gitlab-org/gitlab@master

68 files changed, 606 insertions, 1495 deletions

diff --git a/app/assets/javascripts/behaviors/markdown/copy_as_gfm.js b/app/assets/javascripts/behaviors/markdown/copy_as_gfm.js
index 72aae254584..7e5a51a825f 100644
--- a/app/assets/javascripts/behaviors/markdown/copy_as_gfm.js
+++ b/app/assets/javascripts/behaviors/markdown/copy_as_gfm.js
@@ -161,6 +161,8 @@ export class CopyAsGFM {
       codeElement.appendChild(documentFragment);
     }
 
+    [...codeElement.querySelectorAll('.idiff')].forEach((el) => el.classList.remove('idiff'));
+
     return codeElement;
   }
 
@@ -176,10 +178,10 @@ export class CopyAsGFM {
         wrapEl.appendChild(node.cloneNode(true));
         const doc = DOMParser.fromSchema(schema.default).parse(wrapEl);
 
-        const res = markdownSerializer.default.serialize(doc, {
-          tightLists: true,
-        });
-        return res;
+        return markdownSerializer.default.serialize(
+          { doc },
+          { useCanonicalSrc: false, skipEmptyNodes: true },
+        );
       })
       .catch(() => {});
   }
diff --git a/app/assets/javascripts/behaviors/markdown/editor_extensions.js b/app/assets/javascripts/behaviors/markdown/editor_extensions.js
deleted file mode 100644
index 165031c3e7d..00000000000
--- a/app/assets/javascripts/behaviors/markdown/editor_extensions.js
+++ /dev/null
@@ -1,95 +0,0 @@
-import Bold from './marks/bold';
-import Code from './marks/code';
-import InlineDiff from './marks/inline_diff';
-import InlineHTML from './marks/inline_html';
-import Italic from './marks/italic';
-import Link from './marks/link';
-import MathMark from './marks/math';
-import Strike from './marks/strike';
-import Audio from './nodes/audio';
-import Blockquote from './nodes/blockquote';
-import BulletList from './nodes/bullet_list';
-import CodeBlock from './nodes/code_block';
-import DescriptionDetails from './nodes/description_details';
-import DescriptionList from './nodes/description_list';
-import DescriptionTerm from './nodes/description_term';
-import Details from './nodes/details';
-import Doc from './nodes/doc';
-
-import Emoji from './nodes/emoji';
-import HardBreak from './nodes/hard_break';
-import Heading from './nodes/heading';
-import HorizontalRule from './nodes/horizontal_rule';
-import Image from './nodes/image';
-
-import ListItem from './nodes/list_item';
-import OrderedList from './nodes/ordered_list';
-import OrderedTaskList from './nodes/ordered_task_list';
-import Paragraph from './nodes/paragraph';
-import Reference from './nodes/reference';
-import Summary from './nodes/summary';
-import Table from './nodes/table';
-import TableBody from './nodes/table_body';
-import TableCell from './nodes/table_cell';
-import TableHead from './nodes/table_head';
-import TableHeaderRow from './nodes/table_header_row';
-import TableOfContents from './nodes/table_of_contents';
-import TableRow from './nodes/table_row';
-
-import TaskList from './nodes/task_list';
-import TaskListItem from './nodes/task_list_item';
-import Text from './nodes/text';
-import Video from './nodes/video';
-
-// The filters referenced in lib/banzai/pipeline/gfm_pipeline.rb transform
-// GitLab Flavored Markdown (GFM) to HTML.
-// The nodes and marks referenced here transform that same HTML to GFM to be copied to the clipboard.
-// Every filter in lib/banzai/pipeline/gfm_pipeline.rb that generates HTML
-// from GFM should have a node or mark here.
-// The GFM-to-HTML-to-GFM cycle is tested in spec/features/markdown/copy_as_gfm_spec.rb.
-
-export default {
-  nodes: [
-    Doc(),
-    Paragraph(),
-    Text(),
-
-    Blockquote(),
-    CodeBlock(),
-    HardBreak(),
-    Heading(),
-    HorizontalRule(),
-    Image(),
-
-    Table(),
-    TableHead(),
-    TableBody(),
-    TableHeaderRow(),
-    TableRow(),
-    TableCell(),
-
-    Emoji(),
-    Reference(),
-
-    TableOfContents(),
-    Video(),
-    Audio(),
-
-    BulletList(),
-    OrderedList(),
-    ListItem(),
-
-    DescriptionList(),
-    DescriptionTerm(),
-    DescriptionDetails(),
-
-    TaskList(),
-    OrderedTaskList(),
-    TaskListItem(),
-
-    Summary(),
-    Details(),
-  ],
-
-  marks: [Bold(), Italic(), Strike(), InlineDiff(), Link(), Code(), MathMark(), InlineHTML()],
-};
diff --git a/app/assets/javascripts/behaviors/markdown/marks/bold.js b/app/assets/javascripts/behaviors/markdown/marks/bold.js
deleted file mode 100644
index dd730947a5f..00000000000
--- a/app/assets/javascripts/behaviors/markdown/marks/bold.js
+++ /dev/null
@@ -1,17 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => {
-  return {
-    name: 'bold',
-    schema: {
-      parseDOM: [
-        {
-          tag: 'strong',
-        },
-      ],
-      toDOM: () => ['strong', 0],
-    },
-    toMarkdown: defaultMarkdownSerializer.marks.strong,
-  };
-};
diff --git a/app/assets/javascripts/behaviors/markdown/marks/code.js b/app/assets/javascripts/behaviors/markdown/marks/code.js
deleted file mode 100644
index ea5af8b4a1f..00000000000
--- a/app/assets/javascripts/behaviors/markdown/marks/code.js
+++ /dev/null
@@ -1,12 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'code',
-  schema: {
-    excludes: '_',
-    parseDOM: [{ tag: 'code' }],
-    toDOM: () => ['code', 0],
-  },
-  toMarkdown: defaultMarkdownSerializer.marks.code,
-});
diff --git a/app/assets/javascripts/behaviors/markdown/marks/inline_diff.js b/app/assets/javascripts/behaviors/markdown/marks/inline_diff.js
deleted file mode 100644
index 69d345c81e4..00000000000
--- a/app/assets/javascripts/behaviors/markdown/marks/inline_diff.js
+++ /dev/null
@@ -1,29 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::InlineDiffFilter
-export default () => ({
-  name: 'inline_diff',
-  schema: {
-    attrs: {
-      addition: {
-        default: true,
-      },
-    },
-    parseDOM: [
-      { tag: 'span.idiff.addition', attrs: { addition: true } },
-      { tag: 'span.idiff.deletion', attrs: { addition: false } },
-    ],
-    toDOM: (node) => [
-      'span',
-      { class: `idiff left right ${node.attrs.addition ? 'addition' : 'deletion'}` },
-      0,
-    ],
-  },
-  toMarkdown: {
-    mixable: true,
-    open(_, mark) {
-      return mark.attrs.addition ? '{+' : '{-';
-    },
-    close(_, mark) {
-      return mark.attrs.addition ? '+}' : '-}';
-    },
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/marks/inline_html.js b/app/assets/javascripts/behaviors/markdown/marks/inline_html.js
deleted file mode 100644
index 4520598e0ab..00000000000
--- a/app/assets/javascripts/behaviors/markdown/marks/inline_html.js
+++ /dev/null
@@ -1,35 +0,0 @@
-import { escape } from 'lodash';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'inline_html',
-  schema: {
-    excludes: '',
-    attrs: {
-      tag: {},
-      title: { default: null },
-    },
-    parseDOM: [
-      {
-        tag: 'sup, sub, kbd, q, samp, var',
-        getAttrs: (el) => ({ tag: el.nodeName.toLowerCase() }),
-      },
-      {
-        tag: 'abbr',
-        getAttrs: (el) => ({ tag: 'abbr', title: el.getAttribute('title') }),
-      },
-    ],
-    toDOM: (node) => [node.attrs.tag, { title: node.attrs.title }, 0],
-  },
-  toMarkdown: {
-    mixable: true,
-    open(state, mark) {
-      return `<${mark.attrs.tag}${
-        mark.attrs.title ? ` title="${state.esc(escape(mark.attrs.title))}"` : ''
-      }>`;
-    },
-    close(_, mark) {
-      return `</${mark.attrs.tag}>`;
-    },
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/marks/italic.js b/app/assets/javascripts/behaviors/markdown/marks/italic.js
deleted file mode 100644
index 3ec8f0071e9..00000000000
--- a/app/assets/javascripts/behaviors/markdown/marks/italic.js
+++ /dev/null
@@ -1,11 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'italic',
-  schema: {
-    parseDOM: [{ tag: 'em' }],
-    toDOM: () => ['em', 0],
-  },
-  toMarkdown: defaultMarkdownSerializer.marks.em,
-});
diff --git a/app/assets/javascripts/behaviors/markdown/marks/link.js b/app/assets/javascripts/behaviors/markdown/marks/link.js
deleted file mode 100644
index 977453fee01..00000000000
--- a/app/assets/javascripts/behaviors/markdown/marks/link.js
+++ /dev/null
@@ -1,47 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'link',
-  schema: {
-    attrs: {
-      href: {
-        default: null,
-      },
-      target: {
-        default: null,
-      },
-    },
-    inclusive: false,
-    parseDOM: [
-      {
-        tag: 'a[href]',
-        getAttrs: (dom) => ({
-          href: dom.getAttribute('href'),
-          target: dom.getAttribute('target'),
-        }),
-      },
-    ],
-    toDOM: (node) => [
-      'a',
-      {
-        ...node.attrs,
-        // eslint-disable-next-line @gitlab/require-i18n-strings
-        rel: 'noopener noreferrer nofollow',
-        target: node.attrs.target,
-      },
-      0,
-    ],
-  },
-  toMarkdown: {
-    mixable: true,
-    open(state, mark, parent, index) {
-      const open = defaultMarkdownSerializer.marks.link.open(state, mark, parent, index);
-      return open === '<' ? '' : open;
-    },
-    close(state, mark, parent, index) {
-      const close = defaultMarkdownSerializer.marks.link.close(state, mark, parent, index);
-      return close === '>' ? '' : close;
-    },
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/marks/math.js b/app/assets/javascripts/behaviors/markdown/marks/math.js
deleted file mode 100644
index a50a649b6eb..00000000000
--- a/app/assets/javascripts/behaviors/markdown/marks/math.js
+++ /dev/null
@@ -1,31 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-import { HIGHER_PARSE_RULE_PRIORITY } from '../constants';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MathFilter
-export default () => ({
-  name: 'math',
-  schema: {
-    parseDOM: [
-      // Matches HTML generated by Banzai::Filter::MathFilter
-      {
-        tag: 'code.code.math[data-math-style=inline]',
-        priority: HIGHER_PARSE_RULE_PRIORITY,
-      },
-      // Matches HTML after being transformed by app/assets/javascripts/behaviors/markdown/render_math.js
-      {
-        tag: 'span.katex',
-        contentElement: 'annotation[encoding="application/x-tex"]',
-      },
-    ],
-    toDOM: () => ['code', { class: 'code math', 'data-math-style': 'inline' }, 0],
-  },
-  toMarkdown: {
-    escape: false,
-    open(state, mark, parent, index) {
-      return `$${defaultMarkdownSerializer.marks.code.open(state, mark, parent, index)}`;
-    },
-    close(state, mark, parent, index) {
-      return `${defaultMarkdownSerializer.marks.code.close(state, mark, parent, index)}$`;
-    },
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/marks/strike.js b/app/assets/javascripts/behaviors/markdown/marks/strike.js
deleted file mode 100644
index afab266b645..00000000000
--- a/app/assets/javascripts/behaviors/markdown/marks/strike.js
+++ /dev/null
@@ -1,37 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'strike',
-  schema: {
-    attrs: {
-      strike: {
-        default: false,
-      },
-      inapplicable: {
-        default: false,
-      },
-    },
-    parseDOM: [
-      { tag: 'li.inapplicable > s', attrs: { inapplicable: true } },
-      { tag: 'li.inapplicable > p:first-of-type > s', attrs: { inapplicable: true } },
-      { tag: 's', attrs: { strike: true } },
-      { tag: 'del' },
-    ],
-    toDOM: () => ['s', 0],
-  },
-  toMarkdown: {
-    open(_, mark) {
-      if (mark.attrs.strike) {
-        return '<s>';
-      }
-      return mark.attrs.inapplicable ? '' : '~~';
-    },
-    close(_, mark) {
-      if (mark.attrs.strike) {
-        return '</s>';
-      }
-      return mark.attrs.inapplicable ? '' : '~~';
-    },
-    mixable: true,
-    expelEnclosingWhitespace: true,
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/audio.js b/app/assets/javascripts/behaviors/markdown/nodes/audio.js
deleted file mode 100644
index 97ab86c6d23..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/audio.js
+++ /dev/null
@@ -1,4 +0,0 @@
-import playable from './playable';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::AudioLinkFilter
-export default () => playable({ mediaType: 'audio' });
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/blockquote.js b/app/assets/javascripts/behaviors/markdown/nodes/blockquote.js
deleted file mode 100644
index 6a4552d47e4..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/blockquote.js
+++ /dev/null
@@ -1,19 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'blockquote',
-  schema: {
-    content: 'block*',
-    group: 'block',
-    defining: true,
-    draggable: false,
-    parseDOM: [{ tag: 'blockquote' }],
-    toDOM: () => ['blockquote', 0],
-  },
-  toMarkdown(state, node) {
-    if (!node.childCount) return;
-
-    defaultMarkdownSerializer.nodes.blockquote(state, node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/bullet_list.js b/app/assets/javascripts/behaviors/markdown/nodes/bullet_list.js
deleted file mode 100644
index 95cd3605da5..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/bullet_list.js
+++ /dev/null
@@ -1,15 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'bullet_list',
-  schema: {
-    content: 'list_item+',
-    group: 'block',
-    parseDOM: [{ tag: 'ul' }],
-    toDOM: () => ['ul', 0],
-  },
-  toMarkdown(state, node) {
-    defaultMarkdownSerializer.nodes.bullet_list(state, node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/code_block.js b/app/assets/javascripts/behaviors/markdown/nodes/code_block.js
deleted file mode 100644
index b862d111de7..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/code_block.js
+++ /dev/null
@@ -1,94 +0,0 @@
-const PLAINTEXT_LANG = 'plaintext';
-
-// Transforms generated HTML back to GFM for:
-// - Banzai::Filter::SyntaxHighlightFilter
-// - Banzai::Filter::MathFilter
-// - Banzai::Filter::MermaidFilter
-// - Banzai::Filter::SuggestionFilter
-export default () => ({
-  name: 'code_block',
-  schema: {
-    content: 'text*',
-    marks: '',
-    group: 'block',
-    code: true,
-    defining: true,
-    attrs: {
-      lang: { default: PLAINTEXT_LANG },
-    },
-    parseDOM: [
-      // Matches HTML generated by Banzai::Filter::SyntaxHighlightFilter, Banzai::Filter::MathFilter, Banzai::Filter::MermaidFilter, or Banzai::Filter::SuggestionFilter
-      {
-        tag: 'pre.code.highlight',
-        preserveWhitespace: 'full',
-        getAttrs: (el) => {
-          const lang = el.getAttribute('lang');
-          if (!lang || lang === '') return {};
-
-          return { lang };
-        },
-      },
-      // Matches HTML generated by Banzai::Filter::MathFilter,
-      // after being transformed by app/assets/javascripts/behaviors/markdown/render_math.js
-      {
-        tag: 'span.katex-display',
-        preserveWhitespace: 'full',
-        contentElement: 'annotation[encoding="application/x-tex"]',
-        attrs: { lang: 'math' },
-      },
-      // Matches HTML generated by Banzai::Filter::MermaidFilter,
-      // after being transformed by app/assets/javascripts/behaviors/markdown/render_sandboxed_mermaid.js
-      {
-        tag: 'svg.mermaid',
-        preserveWhitespace: 'full',
-        contentElement: 'text.source',
-        attrs: { lang: 'mermaid' },
-      },
-      // Matches HTML generated by Banzai::Filter::SuggestionFilter,
-      // after being transformed by app/assets/javascripts/vue_shared/components/markdown/suggestions.vue
-      {
-        tag: '.md-suggestion',
-        skip: true,
-      },
-      {
-        tag: '.md-suggestion-header',
-        ignore: true,
-      },
-      {
-        tag: '.md-suggestion-diff',
-        preserveWhitespace: 'full',
-        getContent: (el, schema) =>
-          [...el.querySelectorAll('.line_content.new span')].map((span) =>
-            schema.text(span.innerText),
-          ),
-        attrs: { lang: 'suggestion' },
-      },
-    ],
-    toDOM: (node) => ['pre', { class: 'code highlight', lang: node.attrs.lang }, ['code', 0]],
-  },
-
-  toMarkdown(state, node) {
-    if (!node.childCount) return;
-
-    const {
-      textContent: text,
-      attrs: { lang },
-    } = node;
-
-    // Prefixes lines with 4 spaces if the code contains a line that starts with triple backticks
-    if (lang === PLAINTEXT_LANG && text.match(/^```/gm)) {
-      state.wrapBlock('    ', null, node, () => state.text(text, false));
-      return;
-    }
-
-    state.write('```');
-    if (lang !== PLAINTEXT_LANG) state.write(lang);
-
-    state.ensureNewLine();
-    state.text(text, false);
-    state.ensureNewLine();
-
-    state.write('```');
-    state.closeBlock(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/description_details.js b/app/assets/javascripts/behaviors/markdown/nodes/description_details.js
deleted file mode 100644
index 20760286045..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/description_details.js
+++ /dev/null
@@ -1,20 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'description_details',
-
-  schema: {
-    content: 'text*',
-    marks: '',
-    defining: true,
-    parseDOM: [{ tag: 'dd' }],
-    toDOM: () => ['dd', 0],
-  },
-
-  toMarkdown(state, node) {
-    state.flushClose(1);
-    state.write('<dd>');
-    state.text(node.textContent, false);
-    state.write('</dd>');
-    state.closeBlock(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/description_list.js b/app/assets/javascripts/behaviors/markdown/nodes/description_list.js
deleted file mode 100644
index c5305c48423..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/description_list.js
+++ /dev/null
@@ -1,19 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'description_list',
-  schema: {
-    content: '(description_term+ description_details+)+',
-    group: 'block',
-    parseDOM: [{ tag: 'dl' }],
-    toDOM: () => ['dl', 0],
-  },
-
-  toMarkdown(state, node) {
-    state.write('<dl>\n');
-    state.wrapBlock('  ', null, node, () => state.renderContent(node));
-    state.flushClose(1);
-    state.ensureNewLine();
-    state.write('</dl>');
-    state.closeBlock(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/description_term.js b/app/assets/javascripts/behaviors/markdown/nodes/description_term.js
deleted file mode 100644
index f78f7f13fc4..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/description_term.js
+++ /dev/null
@@ -1,18 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'description_term',
-  schema: {
-    content: 'text*',
-    marks: '',
-    defining: true,
-    parseDOM: [{ tag: 'dt' }],
-    toDOM: () => ['dt', 0],
-  },
-  toMarkdown(state, node) {
-    state.flushClose(state.closed && state.closed.type === node.type ? 1 : 2);
-    state.write('<dt>');
-    state.text(node.textContent, false);
-    state.write('</dt>');
-    state.closeBlock(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/details.js b/app/assets/javascripts/behaviors/markdown/nodes/details.js
deleted file mode 100644
index 9fb0d60b93a..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/details.js
+++ /dev/null
@@ -1,18 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'details',
-  schema: {
-    content: 'summary block*',
-    group: 'block',
-    parseDOM: [{ tag: 'details' }],
-    toDOM: () => ['details', { open: true, onclick: 'return false', tabindex: '-1' }, 0],
-  },
-  toMarkdown(state, node) {
-    state.write('<details>\n');
-    state.renderContent(node);
-    state.flushClose(1);
-    state.ensureNewLine();
-    state.write('</details>');
-    state.closeBlock(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/doc.js b/app/assets/javascripts/behaviors/markdown/nodes/doc.js
deleted file mode 100644
index 3101e6e0e3a..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/doc.js
+++ /dev/null
@@ -1,6 +0,0 @@
-export default () => ({
-  name: 'doc',
-  schema: {
-    content: 'block+',
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/emoji.js b/app/assets/javascripts/behaviors/markdown/nodes/emoji.js
deleted file mode 100644
index 086c277bad4..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/emoji.js
+++ /dev/null
@@ -1,43 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::EmojiFilter
-export default () => ({
-  name: 'emoji',
-  schema: {
-    inline: true,
-    group: 'inline',
-    attrs: {
-      name: {},
-      title: {},
-      moji: {},
-    },
-    parseDOM: [
-      {
-        tag: 'gl-emoji',
-        getAttrs: (el) => ({
-          name: el.dataset.name,
-          title: el.getAttribute('title'),
-          moji: el.textContent,
-        }),
-      },
-      {
-        tag: 'img.emoji',
-        getAttrs: (el) => {
-          const name = el.getAttribute('title').replace(/^:|:$/g, '');
-
-          return {
-            name,
-            title: name,
-            moji: name,
-          };
-        },
-      },
-    ],
-    toDOM: (node) => [
-      'gl-emoji',
-      { 'data-name': node.attrs.name, title: node.attrs.title },
-      node.attrs.moji,
-    ],
-  },
-  toMarkdown(state, node) {
-    state.write(`:${node.attrs.name}:`);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/hard_break.js b/app/assets/javascripts/behaviors/markdown/nodes/hard_break.js
deleted file mode 100644
index 1668af9c3f4..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/hard_break.js
+++ /dev/null
@@ -1,14 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'hard_break',
-  schema: {
-    inline: true,
-    group: 'inline',
-    selectable: false,
-    parseDOM: [{ tag: 'br' }],
-    toDOM: () => ['br'],
-  },
-  toMarkdown(state) {
-    if (!state.atBlank()) state.write('  \n');
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/heading.js b/app/assets/javascripts/behaviors/markdown/nodes/heading.js
deleted file mode 100644
index 21b4ec69b70..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/heading.js
+++ /dev/null
@@ -1,27 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default ({ levels = [1, 2, 3, 4, 5, 6] } = {}) => ({
-  name: 'heading',
-  schema: {
-    attrs: {
-      level: {
-        default: 1,
-      },
-    },
-    content: 'inline*',
-    group: 'block',
-    defining: true,
-    draggable: false,
-    parseDOM: levels.map((level) => ({
-      tag: `h${level}`,
-      attrs: { level },
-    })),
-    toDOM: (node) => [`h${node.attrs.level}`, 0],
-  },
-  toMarkdown(state, node) {
-    if (!node.childCount) return;
-
-    defaultMarkdownSerializer.nodes.heading(state, node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/horizontal_rule.js b/app/assets/javascripts/behaviors/markdown/nodes/horizontal_rule.js
deleted file mode 100644
index 2d7074e567f..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/horizontal_rule.js
+++ /dev/null
@@ -1,14 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'horizontal_rule',
-  schema: {
-    group: 'block',
-    parseDOM: [{ tag: 'hr' }],
-    toDOM: () => ['hr'],
-  },
-  toMarkdown(state, node) {
-    defaultMarkdownSerializer.nodes.horizontal_rule(state, node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/image.js b/app/assets/javascripts/behaviors/markdown/nodes/image.js
deleted file mode 100644
index 370cc347a05..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/image.js
+++ /dev/null
@@ -1,48 +0,0 @@
-import { placeholderImage } from '~/lazy_loader';
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-import { HIGHER_PARSE_RULE_PRIORITY } from '../constants';
-
-export default () => ({
-  name: 'image',
-  schema: {
-    attrs: {
-      src: {},
-      alt: {
-        default: null,
-      },
-      title: {
-        default: null,
-      },
-    },
-    group: 'inline',
-    inline: true,
-    draggable: true,
-    parseDOM: [
-      // Matches HTML generated by Banzai::Filter::ImageLinkFilter
-      {
-        tag: 'a.no-attachment-icon',
-        priority: HIGHER_PARSE_RULE_PRIORITY,
-        skip: true,
-      },
-      // Matches HTML generated by Banzai::Filter::ImageLazyLoadFilter
-      {
-        tag: 'img[src]:not(.emoji)',
-        getAttrs: (el) => {
-          const imageSrc = el.src;
-          const imageUrl =
-            imageSrc && imageSrc !== placeholderImage ? imageSrc : el.dataset.src || '';
-
-          return {
-            src: imageUrl,
-            title: el.getAttribute('title'),
-            alt: el.getAttribute('alt'),
-          };
-        },
-      },
-    ],
-    toDOM: (node) => ['img', node.attrs],
-  },
-  toMarkdown(state, node) {
-    defaultMarkdownSerializer.nodes.image(state, node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/list_item.js b/app/assets/javascripts/behaviors/markdown/nodes/list_item.js
deleted file mode 100644
index 97c1f07427d..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/list_item.js
+++ /dev/null
@@ -1,16 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'list_item',
-  schema: {
-    content: 'paragraph block*',
-    defining: true,
-    draggable: false,
-    parseDOM: [{ tag: 'li' }],
-    toDOM: () => ['li', 0],
-  },
-  toMarkdown(state, node) {
-    defaultMarkdownSerializer.nodes.list_item(state, node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/ordered_list.js b/app/assets/javascripts/behaviors/markdown/nodes/ordered_list.js
deleted file mode 100644
index f2f3eff266a..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/ordered_list.js
+++ /dev/null
@@ -1,25 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'ordered_list',
-  schema: {
-    attrs: {
-      order: {
-        default: 1,
-      },
-    },
-    content: 'list_item+',
-    group: 'block',
-    parseDOM: [
-      {
-        tag: 'ol',
-        getAttrs: (dom) => ({
-          order: dom.hasAttribute('start') ? dom.getAttribute('start') + 1 : 1,
-        }),
-      },
-    ],
-    toDOM: (node) => (node.attrs.order === 1 ? ['ol', 0] : ['ol', { start: node.attrs.order }, 0]),
-  },
-  toMarkdown(state, node) {
-    state.renderList(node, '   ', () => '1. ');
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/ordered_task_list.js b/app/assets/javascripts/behaviors/markdown/nodes/ordered_task_list.js
deleted file mode 100644
index 53a6a0d9e07..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/ordered_task_list.js
+++ /dev/null
@@ -1,21 +0,0 @@
-import { HIGHER_PARSE_RULE_PRIORITY } from '../constants';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::TaskListFilter
-export default () => ({
-  name: 'ordered_task_list',
-  schema: {
-    group: 'block',
-    content: '(task_list_item|list_item)+',
-    parseDOM: [
-      {
-        priority: HIGHER_PARSE_RULE_PRIORITY,
-        tag: 'ol.task-list',
-      },
-    ],
-    toDOM: () => ['ol', { class: 'task-list' }, 0],
-  },
-
-  toMarkdown(state, node) {
-    state.renderList(node, '   ', () => '1. ');
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/paragraph.js b/app/assets/javascripts/behaviors/markdown/nodes/paragraph.js
deleted file mode 100644
index 310feebb390..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/paragraph.js
+++ /dev/null
@@ -1,15 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'paragraph',
-  schema: {
-    content: 'inline*',
-    group: 'block',
-    parseDOM: [{ tag: 'p' }],
-    toDOM: () => ['p', 0],
-  },
-  toMarkdown(state, node) {
-    defaultMarkdownSerializer.nodes.paragraph(state, node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/playable.js b/app/assets/javascripts/behaviors/markdown/nodes/playable.js
deleted file mode 100644
index 7559c2a6a8a..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/playable.js
+++ /dev/null
@@ -1,56 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-
-/**
- * Abstract base class for playable media, like video and audio.
- * Must not be instantiated directly. Subclasses must set
- * the `mediaType` property in their constructors.
- * @abstract
- */
-export default ({ mediaType, extraElementAttrs = {} }) => {
-  const attrs = {
-    src: {},
-    alt: {
-      default: null,
-    },
-  };
-  const parseDOM = [
-    {
-      // eslint-disable-next-line @gitlab/require-i18n-strings
-      tag: `.${mediaType}-container`,
-      getAttrs: (el) => ({
-        src: el.querySelector(mediaType).src,
-        alt: el.querySelector(mediaType).dataset.title,
-      }),
-    },
-  ];
-  const toDOM = (node) => [
-    'span',
-    { class: `media-container ${mediaType}-container` },
-    [
-      mediaType,
-      {
-        src: node.attrs.src,
-        controls: true,
-        'data-setup': '{}',
-        'data-title': node.attrs.alt,
-        ...extraElementAttrs,
-      },
-    ],
-    ['a', { href: node.attrs.src }, node.attrs.alt],
-  ];
-
-  return {
-    name: mediaType,
-    schema: {
-      attrs,
-      group: 'inline',
-      inline: true,
-      draggable: true,
-      parseDOM,
-      toDOM,
-    },
-    toMarkdown(state, node) {
-      defaultMarkdownSerializer.nodes.image(state, node);
-    },
-  };
-};
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/reference.js b/app/assets/javascripts/behaviors/markdown/nodes/reference.js
deleted file mode 100644
index 9ae6ab07004..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/reference.js
+++ /dev/null
@@ -1,44 +0,0 @@
-import { HIGHER_PARSE_RULE_PRIORITY } from '../constants';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::ReferenceFilter and subclasses
-export default () => ({
-  name: 'reference',
-  schema: {
-    inline: true,
-    group: 'inline',
-    atom: true,
-    attrs: {
-      className: {},
-      referenceType: {},
-      originalText: { default: null },
-      href: {},
-      text: {},
-    },
-    parseDOM: [
-      {
-        tag: 'a.gfm:not([data-link=true])',
-        priority: HIGHER_PARSE_RULE_PRIORITY,
-        getAttrs: (el) => ({
-          className: el.className,
-          referenceType: el.dataset.referenceType,
-          originalText: el.dataset.original,
-          href: el.getAttribute('href'),
-          text: el.textContent,
-        }),
-      },
-    ],
-    toDOM: (node) => [
-      'a',
-      {
-        class: node.attrs.className,
-        href: node.attrs.href,
-        'data-reference-type': node.attrs.referenceType,
-        'data-original': node.attrs.originalText,
-      },
-      node.attrs.text,
-    ],
-  },
-  toMarkdown(state, node) {
-    state.write(node.attrs.originalText || node.attrs.text);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/summary.js b/app/assets/javascripts/behaviors/markdown/nodes/summary.js
deleted file mode 100644
index eb91b3c981e..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/summary.js
+++ /dev/null
@@ -1,17 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'summary',
-  schema: {
-    content: 'text*',
-    marks: '',
-    defining: true,
-    parseDOM: [{ tag: 'summary' }],
-    toDOM: () => ['summary', 0],
-  },
-  toMarkdown(state, node) {
-    state.write('<summary>');
-    state.text(node.textContent, false);
-    state.write('</summary>');
-    state.closeBlock(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/table.js b/app/assets/javascripts/behaviors/markdown/nodes/table.js
deleted file mode 100644
index c766f7f1fba..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/table.js
+++ /dev/null
@@ -1,15 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'table',
-  schema: {
-    content: 'table_head table_body',
-    group: 'block',
-    isolating: true,
-    parseDOM: [{ tag: 'table' }],
-    toDOM: () => ['table', 0],
-  },
-  toMarkdown(state, node) {
-    state.renderContent(node);
-    state.closeBlock(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/table_body.js b/app/assets/javascripts/behaviors/markdown/nodes/table_body.js
deleted file mode 100644
index 0a49fb558ae..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/table_body.js
+++ /dev/null
@@ -1,14 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'table_body',
-  schema: {
-    content: 'table_row+',
-    parseDOM: [{ tag: 'tbody' }],
-    toDOM: () => ['tbody', 0],
-  },
-  toMarkdown: (state, node) => {
-    state.flushClose(1);
-    state.renderContent(node);
-    state.closeBlock(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/table_cell.js b/app/assets/javascripts/behaviors/markdown/nodes/table_cell.js
deleted file mode 100644
index f46344ba43c..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/table_cell.js
+++ /dev/null
@@ -1,25 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'table_cell',
-  schema: {
-    attrs: {
-      header: { default: false },
-      align: { default: null },
-    },
-    content: 'inline*',
-    isolating: true,
-    parseDOM: [
-      {
-        tag: 'td, th',
-        getAttrs: (el) => ({
-          header: el.tagName === 'TH',
-          align: el.getAttribute('align') || el.style.textAlign,
-        }),
-      },
-    ],
-    toDOM: (node) => [node.attrs.header ? 'th' : 'td', { align: node.attrs.align }, 0],
-  },
-  toMarkdown: (state, node) => {
-    state.renderInline(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/table_head.js b/app/assets/javascripts/behaviors/markdown/nodes/table_head.js
deleted file mode 100644
index 2e9b53ee0ac..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/table_head.js
+++ /dev/null
@@ -1,14 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'table_head',
-  schema: {
-    content: 'table_header_row',
-    parseDOM: [{ tag: 'thead' }],
-    toDOM: () => ['thead', 0],
-  },
-  toMarkdown: (state, node) => {
-    state.flushClose(1);
-    state.renderContent(node);
-    state.closeBlock(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/table_header_row.js b/app/assets/javascripts/behaviors/markdown/nodes/table_header_row.js
deleted file mode 100644
index d8aa497066c..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/table_header_row.js
+++ /dev/null
@@ -1,36 +0,0 @@
-import { HIGHER_PARSE_RULE_PRIORITY } from '../constants';
-import TableRow from './table_row';
-
-const CENTER_ALIGN = 'center';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'table_header_row',
-  schema: {
-    content: 'table_cell+',
-    parseDOM: [
-      {
-        tag: 'thead tr',
-        priority: HIGHER_PARSE_RULE_PRIORITY,
-      },
-    ],
-    toDOM: () => ['tr', 0],
-  },
-  toMarkdown: (state, node) => {
-    const cellWidths = TableRow().toMarkdown(state, node);
-
-    state.flushClose(1);
-
-    state.write('|');
-    node.forEach((cell, _, i) => {
-      if (i) state.write('|');
-
-      state.write(cell.attrs.align === CENTER_ALIGN ? ':' : '-');
-      state.write(state.repeat('-', cellWidths[i]));
-      state.write(cell.attrs.align === CENTER_ALIGN || cell.attrs.align === 'right' ? ':' : '-');
-    });
-    state.write('|');
-
-    state.closeBlock(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/table_of_contents.js b/app/assets/javascripts/behaviors/markdown/nodes/table_of_contents.js
deleted file mode 100644
index 4a0256c4644..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/table_of_contents.js
+++ /dev/null
@@ -1,26 +0,0 @@
-import { __ } from '~/locale';
-import { HIGHER_PARSE_RULE_PRIORITY } from '../constants';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::TableOfContentsFilter
-export default () => ({
-  name: 'table_of_contents',
-  schema: {
-    group: 'block',
-    atom: true,
-    parseDOM: [
-      {
-        tag: 'ul.section-nav',
-        priority: HIGHER_PARSE_RULE_PRIORITY,
-      },
-      {
-        tag: 'p.table-of-contents',
-        priority: HIGHER_PARSE_RULE_PRIORITY,
-      },
-    ],
-    toDOM: () => ['p', { class: 'table-of-contents' }, __('Table of Contents')],
-  },
-  toMarkdown: (state, node) => {
-    state.write('[[_TOC_]]');
-    state.closeBlock(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/table_row.js b/app/assets/javascripts/behaviors/markdown/nodes/table_row.js
deleted file mode 100644
index 3830dae4f0d..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/table_row.js
+++ /dev/null
@@ -1,28 +0,0 @@
-// Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
-export default () => ({
-  name: 'table_row',
-  schema: {
-    content: 'table_cell+',
-    parseDOM: [{ tag: 'tr' }],
-    toDOM: () => ['tr', 0],
-  },
-  toMarkdown: (state, node) => {
-    const cellWidths = [];
-
-    state.flushClose(1);
-
-    state.write('| ');
-    node.forEach((cell, _, i) => {
-      if (i) state.write(' | ');
-
-      const { length } = state.out;
-      state.render(cell, node, i);
-      cellWidths.push(state.out.length - length);
-    });
-    state.write(' |');
-
-    state.closeBlock(node);
-
-    return cellWidths;
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/task_list.js b/app/assets/javascripts/behaviors/markdown/nodes/task_list.js
deleted file mode 100644
index 3c3812ad8f7..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/task_list.js
+++ /dev/null
@@ -1,20 +0,0 @@
-import { HIGHER_PARSE_RULE_PRIORITY } from '../constants';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::TaskListFilter
-export default () => ({
-  name: 'task_list',
-  schema: {
-    group: 'block',
-    content: '(task_list_item|list_item)+',
-    parseDOM: [
-      {
-        priority: HIGHER_PARSE_RULE_PRIORITY,
-        tag: 'ul.task-list',
-      },
-    ],
-    toDOM: () => ['ul', { class: 'task-list' }, 0],
-  },
-  toMarkdown(state, node) {
-    state.renderList(node, '  ', () => '* ');
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/task_list_item.js b/app/assets/javascripts/behaviors/markdown/nodes/task_list_item.js
deleted file mode 100644
index e1c1bd58ee2..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/task_list_item.js
+++ /dev/null
@@ -1,71 +0,0 @@
-import { HIGHER_PARSE_RULE_PRIORITY } from '../constants';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::TaskListFilter
-export default () => ({
-  name: 'task_list_item',
-  schema: {
-    attrs: {
-      state: {
-        default: null,
-      },
-    },
-    defining: true,
-    draggable: false,
-    content: 'paragraph block*',
-    parseDOM: [
-      {
-        priority: HIGHER_PARSE_RULE_PRIORITY,
-        tag: 'li.task-list-item',
-        getAttrs: (el) => {
-          const checkbox = el.querySelector('input[type=checkbox].task-list-item-checkbox');
-          if (checkbox?.matches('[data-inapplicable]')) {
-            return { state: 'inapplicable' };
-          }
-          if (checkbox?.checked) {
-            return { state: 'done' };
-          }
-
-          return {};
-        },
-      },
-    ],
-    toDOM(node) {
-      return [
-        'li',
-        {
-          class: () => {
-            if (node.attrs.state === 'inapplicable') {
-              return 'task-list-item inapplicable';
-            }
-
-            return 'task-list-item';
-          },
-        },
-        [
-          'input',
-          {
-            type: 'checkbox',
-            class: 'task-list-item-checkbox',
-            checked: node.attrs.state === 'done',
-            'data-inapplicable': node.attrs.state === 'inapplicable',
-          },
-        ],
-        ['div', { class: 'todo-content' }, 0],
-      ];
-    },
-  },
-  toMarkdown(state, node) {
-    switch (node.attrs.state) {
-      case 'done':
-        state.write('[x] ');
-        break;
-      case 'inapplicable':
-        state.write('[~] ');
-        break;
-      default:
-        state.write('[ ] ');
-        break;
-    }
-    state.renderContent(node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/text.js b/app/assets/javascripts/behaviors/markdown/nodes/text.js
deleted file mode 100644
index 0e1f0bc0e40..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/text.js
+++ /dev/null
@@ -1,11 +0,0 @@
-import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-
-export default () => ({
-  name: 'text',
-  schema: {
-    group: 'inline',
-  },
-  toMarkdown(state, node) {
-    defaultMarkdownSerializer.nodes.text(state, node);
-  },
-});
diff --git a/app/assets/javascripts/behaviors/markdown/nodes/video.js b/app/assets/javascripts/behaviors/markdown/nodes/video.js
deleted file mode 100644
index aa1088826da..00000000000
--- a/app/assets/javascripts/behaviors/markdown/nodes/video.js
+++ /dev/null
@@ -1,4 +0,0 @@
-import playable from './playable';
-
-// Transforms generated HTML back to GFM for Banzai::Filter::VideoLinkFilter
-export default () => playable({ mediaType: 'video', extraElementAttrs: { width: '400' } });
diff --git a/app/assets/javascripts/behaviors/markdown/schema.js b/app/assets/javascripts/behaviors/markdown/schema.js
index 31bab23c8b0..baccddfc7cd 100644
--- a/app/assets/javascripts/behaviors/markdown/schema.js
+++ b/app/assets/javascripts/behaviors/markdown/schema.js
@@ -1,20 +1,13 @@
+import { flatMap } from 'lodash';
+import { Editor } from '@tiptap/vue-2';
+import OrderedMap from 'orderedmap';
 import { Schema } from '@tiptap/pm/model';
-import editorExtensions from './editor_extensions';
+import * as extensions from '~/content_editor/extensions';
 
-const nodes = editorExtensions.nodes.reduce(
-  (ns, { name, schema }) => ({
-    ...ns,
-    [name]: schema,
-  }),
-  {},
-);
+const { schema } = new Editor({ extensions: flatMap(extensions) });
 
-const marks = editorExtensions.marks.reduce(
-  (ms, { name, schema }) => ({
-    ...ms,
-    [name]: schema,
-  }),
-  {},
-);
+const schemaSpec = { ...schema.spec };
+schemaSpec.marks = OrderedMap.from(schemaSpec.marks).remove('span');
+schemaSpec.nodes = OrderedMap.from(schemaSpec.nodes).remove('div').remove('pre');
 
-export default new Schema({ nodes, marks });
+export default new Schema(schemaSpec);
diff --git a/app/assets/javascripts/behaviors/markdown/serializer.js b/app/assets/javascripts/behaviors/markdown/serializer.js
index e3e8a380cd5..fa21bd4630d 100644
--- a/app/assets/javascripts/behaviors/markdown/serializer.js
+++ b/app/assets/javascripts/behaviors/markdown/serializer.js
@@ -1,20 +1,3 @@
-import { MarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
-import editorExtensions from './editor_extensions';
+import MarkdownSerializer from '~/content_editor/services/markdown_serializer';
 
-const nodes = editorExtensions.nodes.reduce(
-  (ns, { name, toMarkdown }) => ({
-    ...ns,
-    [name]: toMarkdown,
-  }),
-  {},
-);
-
-const marks = editorExtensions.marks.reduce(
-  (ms, { name, toMarkdown }) => ({
-    ...ms,
-    [name]: toMarkdown,
-  }),
-  {},
-);
-
-export default new MarkdownSerializer(nodes, marks);
+export default new MarkdownSerializer();
diff --git a/app/assets/javascripts/content_editor/extensions/code_block_highlight.js b/app/assets/javascripts/content_editor/extensions/code_block_highlight.js
index da5ac7eb158..e75178789da 100644
--- a/app/assets/javascripts/content_editor/extensions/code_block_highlight.js
+++ b/app/assets/javascripts/content_editor/extensions/code_block_highlight.js
@@ -65,6 +65,48 @@ export default CodeBlockLowlight.extend({
         tag: 'pre.js-syntax-highlight',
         preserveWhitespace: 'full',
       },
+      // Matches HTML generated by Banzai::Filter::SyntaxHighlightFilter,
+      // Banzai::Filter::MathFilter, Banzai::Filter::MermaidFilter,
+      // or Banzai::Filter::SuggestionFilter
+      {
+        tag: 'pre.code.highlight',
+        preserveWhitespace: 'full',
+      },
+      // Matches HTML generated by Banzai::Filter::MathFilter,
+      // after being transformed by ~/behaviors/markdown/render_math.js
+      {
+        tag: 'span.katex-display',
+        preserveWhitespace: 'full',
+        contentElement: 'annotation[encoding="application/x-tex"]',
+        attrs: { language: 'math' },
+      },
+      // Matches HTML generated by Banzai::Filter::MermaidFilter,
+      // after being transformed by ~/behaviors/markdown/render_sandboxed_mermaid.js
+      {
+        tag: 'svg.mermaid',
+        preserveWhitespace: 'full',
+        contentElement: 'text.source',
+        attrs: { language: 'mermaid' },
+      },
+      // Matches HTML generated by Banzai::Filter::SuggestionFilter,
+      // after being transformed by ~/vue_shared/components/markdown/suggestions.vue
+      {
+        tag: '.md-suggestion',
+        skip: true,
+      },
+      {
+        tag: '.md-suggestion-header',
+        ignore: true,
+      },
+      {
+        tag: '.md-suggestion-diff',
+        preserveWhitespace: 'full',
+        getContent: (el, schema) =>
+          [...el.querySelectorAll('.line_content.new span')].map((span) =>
+            schema.text(span.innerText),
+          ),
+        attrs: { language: 'suggestion' },
+      },
     ];
   },
   renderHTML({ HTMLAttributes }) {
diff --git a/app/assets/javascripts/content_editor/extensions/code_suggestion.js b/app/assets/javascripts/content_editor/extensions/code_suggestion.js
index c70a96769fb..45090d57559 100644
--- a/app/assets/javascripts/content_editor/extensions/code_suggestion.js
+++ b/app/assets/javascripts/content_editor/extensions/code_suggestion.js
@@ -14,7 +14,7 @@ export default CodeBlockHighlight.extend({
   addOptions() {
     return {
       lowlight,
-      config: {},
+      codeSuggestionsConfig: {},
     };
   },
 
@@ -38,10 +38,13 @@ export default CodeBlockHighlight.extend({
         // do not insert a new suggestion if already inside a suggestion
         if (editor.isActive('codeSuggestion')) return false;
 
-        const rawPath = ext.options.config.diffFile.view_path.replace('/blob/', '/raw/');
+        const rawPath = ext.options.codeSuggestionsConfig.diffFile.view_path.replace(
+          '/blob/',
+          '/raw/',
+        );
         const allLines = (await memoizedGet(rawPath)).split('\n');
-        const { line } = ext.options.config;
-        let { lines } = ext.options.config;
+        const { line } = ext.options.codeSuggestionsConfig;
+        let { lines } = ext.options.codeSuggestionsConfig;
 
         if (!lines.length) lines = [line];
 
diff --git a/app/assets/javascripts/content_editor/extensions/emoji.js b/app/assets/javascripts/content_editor/extensions/emoji.js
index 96e03dfe598..4cfe2c6b06c 100644
--- a/app/assets/javascripts/content_editor/extensions/emoji.js
+++ b/app/assets/javascripts/content_editor/extensions/emoji.js
@@ -1,5 +1,6 @@
 import { Node, InputRule } from '@tiptap/core';
 import { initEmojiMap, getEmojiMap } from '~/emoji';
+import { PARSE_HTML_PRIORITY_HIGHEST } from '../constants';
 
 export default Node.create({
   name: 'emoji',
@@ -12,21 +13,10 @@ export default Node.create({
 
   addAttributes() {
     return {
-      moji: {
-        default: null,
-        parseHTML: (element) => element.textContent,
-      },
-      name: {
-        default: null,
-        parseHTML: (element) => element.dataset.name,
-      },
-      title: {
-        default: null,
-      },
-      unicodeVersion: {
-        default: '6.0',
-        parseHTML: (element) => element.dataset.unicodeVersion,
-      },
+      moji: { default: null },
+      name: { default: null },
+      title: { default: null },
+      unicodeVersion: { default: '6.0' },
     };
   },
 
@@ -34,6 +24,26 @@ export default Node.create({
     return [
       {
         tag: 'gl-emoji',
+        getAttrs: (el) => ({
+          name: el.dataset.name,
+          title: el.getAttribute('title'),
+          moji: el.textContent,
+          unicodeVersion: el.dataset.unicodeVersion || '6.0',
+        }),
+      },
+      {
+        tag: 'img.emoji',
+        getAttrs: (el) => {
+          const name = el.getAttribute('title').replace(/^:|:$/g, '');
+
+          return {
+            name,
+            title: name,
+            moji: name,
+            unicodeVersion: 'custom',
+          };
+        },
+        priority: PARSE_HTML_PRIORITY_HIGHEST,
       },
     ];
   },
diff --git a/app/assets/javascripts/content_editor/extensions/index.js b/app/assets/javascripts/content_editor/extensions/index.js
new file mode 100644
index 00000000000..c611d4aff07
--- /dev/null
+++ b/app/assets/javascripts/content_editor/extensions/index.js
@@ -0,0 +1,62 @@
+export { default as Attachment } from './attachment';
+export { default as Audio } from './audio';
+export { default as Blockquote } from './blockquote';
+export { default as Bold } from './bold';
+export { default as BulletList } from './bullet_list';
+export { default as Code } from './code';
+export { default as CodeBlockHighlight } from './code_block_highlight';
+export { default as CodeSuggestion } from './code_suggestion';
+export { default as ColorChip } from './color_chip';
+export { default as CopyPaste } from './copy_paste';
+export { default as DescriptionItem } from './description_item';
+export { default as DescriptionList } from './description_list';
+export { default as Details } from './details';
+export { default as DetailsContent } from './details_content';
+export { default as Diagram } from './diagram';
+export { default as DrawioDiagram } from './drawio_diagram';
+export { default as Document } from './document';
+export { default as Dropcursor } from './dropcursor';
+export { default as Emoji } from './emoji';
+export { default as ExternalKeydownHandler } from './external_keydown_handler';
+export { default as Figure } from './figure';
+export { default as FigureCaption } from './figure_caption';
+export { default as FootnoteDefinition } from './footnote_definition';
+export { default as FootnoteReference } from './footnote_reference';
+export { default as FootnotesSection } from './footnotes_section';
+export { default as Frontmatter } from './frontmatter';
+export { default as Gapcursor } from './gapcursor';
+export { default as HardBreak } from './hard_break';
+export { default as Heading } from './heading';
+export { default as History } from './history';
+export { default as Highlight } from './highlight';
+export { default as HorizontalRule } from './horizontal_rule';
+export { default as HTMLMarks } from './html_marks';
+export { default as HTMLNodes } from './html_nodes';
+export { default as Image } from './image';
+export { default as InlineDiff } from './inline_diff';
+export { default as Italic } from './italic';
+export { default as Link } from './link';
+export { default as ListItem } from './list_item';
+export { default as Loading } from './loading';
+export { default as MathInline } from './math_inline';
+export { default as OrderedList } from './ordered_list';
+export { default as Paragraph } from './paragraph';
+export { default as Reference } from './reference';
+export { default as ReferenceLabel } from './reference_label';
+export { default as ReferenceDefinition } from './reference_definition';
+export { default as Selection } from './selection';
+export { default as Sourcemap } from './sourcemap';
+export { default as Strike } from './strike';
+export { default as Subscript } from './subscript';
+export { default as Suggestions } from './suggestions';
+export { default as Superscript } from './superscript';
+export { default as Table } from './table';
+export { default as TableCell } from './table_cell';
+export { default as TableHeader } from './table_header';
+export { default as TableOfContents } from './table_of_contents';
+export { default as TableRow } from './table_row';
+export { default as TaskItem } from './task_item';
+export { default as TaskList } from './task_list';
+export { default as Text } from './text';
+export { default as Video } from './video';
+export { default as WordBreak } from './word_break';
diff --git a/app/assets/javascripts/content_editor/extensions/inline_diff.js b/app/assets/javascripts/content_editor/extensions/inline_diff.js
index f76943a0669..905b1f2d42e 100644
--- a/app/assets/javascripts/content_editor/extensions/inline_diff.js
+++ b/app/assets/javascripts/content_editor/extensions/inline_diff.js
@@ -13,7 +13,6 @@ export default Mark.create({
     return {
       type: {
         default: 'addition',
-        parseHTML: (element) => (element.classList.contains('deletion') ? 'deletion' : 'addition'),
       },
     };
   },
@@ -21,7 +20,12 @@ export default Mark.create({
   parseHTML() {
     return [
       {
-        tag: 'span.idiff',
+        tag: 'span.idiff.addition',
+        attrs: { type: 'addition' },
+      },
+      {
+        tag: 'span.idiff.deletion',
+        attrs: { type: 'deletion' },
       },
     ];
   },
diff --git a/app/assets/javascripts/content_editor/extensions/math_inline.js b/app/assets/javascripts/content_editor/extensions/math_inline.js
index 4844f6feb29..b95ef10550f 100644
--- a/app/assets/javascripts/content_editor/extensions/math_inline.js
+++ b/app/assets/javascripts/content_editor/extensions/math_inline.js
@@ -1,15 +1,21 @@
 import { Mark, markInputRule } from '@tiptap/core';
 import { __ } from '~/locale';
-import { PARSE_HTML_PRIORITY_HIGHEST } from '../constants';
+import { PARSE_HTML_PRIORITY_HIGH } from '../constants';
 
 export default Mark.create({
   name: 'mathInline',
 
   parseHTML() {
     return [
+      // Matches HTML generated by Banzai::Filter::MathFilter
       {
         tag: 'code.math[data-math-style=inline]',
-        priority: PARSE_HTML_PRIORITY_HIGHEST,
+        priority: PARSE_HTML_PRIORITY_HIGH,
+      },
+      // Matches HTML after being transformed by app/assets/javascripts/behaviors/markdown/render_math.js
+      {
+        tag: 'span.katex',
+        contentElement: 'annotation[encoding="application/x-tex"]',
       },
     ];
   },
diff --git a/app/assets/javascripts/content_editor/extensions/strike.js b/app/assets/javascripts/content_editor/extensions/strike.js
index b6c9a968fc2..ea1abd35b87 100644
--- a/app/assets/javascripts/content_editor/extensions/strike.js
+++ b/app/assets/javascripts/content_editor/extensions/strike.js
@@ -1 +1,22 @@
-export { Strike as default } from '@tiptap/extension-strike';
+import { Strike } from '@tiptap/extension-strike';
+
+export default Strike.extend({
+  addAttributes() {
+    return {
+      ...this.parent?.(),
+
+      htmlTag: {
+        default: null,
+        renderHTML: () => '',
+      },
+    };
+  },
+
+  parseHTML() {
+    return [
+      { tag: 'del' },
+      { tag: 's', attrs: { htmlTag: 's' } },
+      { tag: 'strike', attrs: { htmlTag: 'strike' } },
+    ];
+  },
+});
diff --git a/app/assets/javascripts/content_editor/extensions/task_item.js b/app/assets/javascripts/content_editor/extensions/task_item.js
index 1e19878be9b..50ea6f393d9 100644
--- a/app/assets/javascripts/content_editor/extensions/task_item.js
+++ b/app/assets/javascripts/content_editor/extensions/task_item.js
@@ -42,7 +42,7 @@ export default TaskItem.extend({
         priority: PARSE_HTML_PRIORITY_HIGHEST,
       },
       {
-        tag: 'li.task-list-item.inapplicable s',
+        tag: 'li.inapplicable > s, li.inapplicable > p:first-of-type > s',
         skip: true,
         priority: PARSE_HTML_PRIORITY_HIGHEST,
       },
diff --git a/app/assets/javascripts/content_editor/services/create_content_editor.js b/app/assets/javascripts/content_editor/services/create_content_editor.js
index 5c48c0b1d43..b7082910161 100644
--- a/app/assets/javascripts/content_editor/services/create_content_editor.js
+++ b/app/assets/javascripts/content_editor/services/create_content_editor.js
@@ -1,69 +1,8 @@
 import { Editor } from '@tiptap/vue-2';
-import { isFunction } from 'lodash';
+import { isFunction, flatMap } from 'lodash';
 import eventHubFactory from '~/helpers/event_hub_factory';
 import { PROVIDE_SERIALIZER_OR_RENDERER_ERROR } from '../constants';
-import Attachment from '../extensions/attachment';
-import Audio from '../extensions/audio';
-import Blockquote from '../extensions/blockquote';
-import Bold from '../extensions/bold';
-import BulletList from '../extensions/bullet_list';
-import Code from '../extensions/code';
-import CodeBlockHighlight from '../extensions/code_block_highlight';
-import CodeSuggestion from '../extensions/code_suggestion';
-import ColorChip from '../extensions/color_chip';
-import CopyPaste from '../extensions/copy_paste';
-import DescriptionItem from '../extensions/description_item';
-import DescriptionList from '../extensions/description_list';
-import Details from '../extensions/details';
-import DetailsContent from '../extensions/details_content';
-import Diagram from '../extensions/diagram';
-import DrawioDiagram from '../extensions/drawio_diagram';
-import Document from '../extensions/document';
-import Dropcursor from '../extensions/dropcursor';
-import Emoji from '../extensions/emoji';
-import ExternalKeydownHandler from '../extensions/external_keydown_handler';
-import Figure from '../extensions/figure';
-import FigureCaption from '../extensions/figure_caption';
-import FootnoteDefinition from '../extensions/footnote_definition';
-import FootnoteReference from '../extensions/footnote_reference';
-import FootnotesSection from '../extensions/footnotes_section';
-import Frontmatter from '../extensions/frontmatter';
-import Gapcursor from '../extensions/gapcursor';
-import HardBreak from '../extensions/hard_break';
-import Heading from '../extensions/heading';
-import History from '../extensions/history';
-import Highlight from '../extensions/highlight';
-import HorizontalRule from '../extensions/horizontal_rule';
-import HTMLMarks from '../extensions/html_marks';
-import HTMLNodes from '../extensions/html_nodes';
-import Image from '../extensions/image';
-import InlineDiff from '../extensions/inline_diff';
-import Italic from '../extensions/italic';
-import Link from '../extensions/link';
-import ListItem from '../extensions/list_item';
-import Loading from '../extensions/loading';
-import MathInline from '../extensions/math_inline';
-import OrderedList from '../extensions/ordered_list';
-import Paragraph from '../extensions/paragraph';
-import Reference from '../extensions/reference';
-import ReferenceLabel from '../extensions/reference_label';
-import ReferenceDefinition from '../extensions/reference_definition';
-import Selection from '../extensions/selection';
-import Sourcemap from '../extensions/sourcemap';
-import Strike from '../extensions/strike';
-import Subscript from '../extensions/subscript';
-import Suggestions from '../extensions/suggestions';
-import Superscript from '../extensions/superscript';
-import Table from '../extensions/table';
-import TableCell from '../extensions/table_cell';
-import TableHeader from '../extensions/table_header';
-import TableOfContents from '../extensions/table_of_contents';
-import TableRow from '../extensions/table_row';
-import TaskItem from '../extensions/task_item';
-import TaskList from '../extensions/task_list';
-import Text from '../extensions/text';
-import Video from '../extensions/video';
-import WordBreak from '../extensions/word_break';
+import * as builtInExtensions from '../extensions';
 import { ContentEditor } from './content_editor';
 import MarkdownSerializer from './markdown_serializer';
 import createGlApiMarkdownDeserializer from './gl_api_markdown_deserializer';
@@ -107,68 +46,18 @@ export const createContentEditor = ({
         render: renderMarkdown,
       });
 
-  const builtInContentEditorExtensions = [
-    Attachment.configure({ uploadsPath, renderMarkdown, eventHub }),
-    Audio,
-    Blockquote,
-    Bold,
-    BulletList,
-    Code,
-    ColorChip,
-    CodeBlockHighlight,
-    CodeSuggestion.configure({ config: codeSuggestionsConfig }),
-    DescriptionItem,
-    DescriptionList,
-    Details,
-    DetailsContent,
-    Document,
-    Diagram,
-    Dropcursor,
-    Emoji,
-    Figure,
-    FigureCaption,
-    FootnoteDefinition,
-    FootnoteReference,
-    FootnotesSection,
-    Frontmatter,
-    Gapcursor,
-    HardBreak,
-    Heading,
-    History,
-    Highlight,
-    HorizontalRule,
-    ...HTMLMarks,
-    ...HTMLNodes,
-    Image,
-    InlineDiff,
-    Italic,
-    ExternalKeydownHandler.configure({ eventHub }),
-    Link,
-    ListItem,
-    Loading,
-    MathInline,
-    OrderedList,
-    Paragraph,
-    CopyPaste.configure({ eventHub, renderMarkdown, serializer }),
-    Reference.configure({ assetResolver }),
-    ReferenceLabel,
-    ReferenceDefinition,
-    Selection,
-    Sourcemap,
-    Strike,
-    Subscript,
-    Superscript,
-    TableCell,
-    TableHeader,
-    TableOfContents,
-    TableRow,
-    Table,
-    TaskItem,
-    TaskList,
-    Text,
-    Video,
-    WordBreak,
-  ];
+  const { Suggestions, DrawioDiagram, ...otherExtensions } = builtInExtensions;
+
+  const builtInContentEditorExtensions = flatMap(otherExtensions).map((ext) =>
+    ext.configure({
+      uploadsPath,
+      renderMarkdown,
+      eventHub,
+      codeSuggestionsConfig,
+      serializer,
+      assetResolver,
+    }),
+  );
 
   const allExtensions = [...builtInContentEditorExtensions, ...extensions];
 
diff --git a/app/assets/javascripts/content_editor/services/markdown_serializer.js b/app/assets/javascripts/content_editor/services/markdown_serializer.js
index 3b759de57f2..5688f30dcc3 100644
--- a/app/assets/javascripts/content_editor/services/markdown_serializer.js
+++ b/app/assets/javascripts/content_editor/services/markdown_serializer.js
@@ -2,56 +2,7 @@ import {
   MarkdownSerializer as ProseMirrorMarkdownSerializer,
   defaultMarkdownSerializer,
 } from '~/lib/prosemirror_markdown_serializer';
-import Audio from '../extensions/audio';
-import Blockquote from '../extensions/blockquote';
-import Bold from '../extensions/bold';
-import BulletList from '../extensions/bullet_list';
-import Code from '../extensions/code';
-import CodeBlockHighlight from '../extensions/code_block_highlight';
-import CodeSuggestion from '../extensions/code_suggestion';
-import DescriptionItem from '../extensions/description_item';
-import DescriptionList from '../extensions/description_list';
-import Details from '../extensions/details';
-import DetailsContent from '../extensions/details_content';
-import DrawioDiagram from '../extensions/drawio_diagram';
-import Diagram from '../extensions/diagram';
-import Emoji from '../extensions/emoji';
-import Figure from '../extensions/figure';
-import FigureCaption from '../extensions/figure_caption';
-import FootnoteDefinition from '../extensions/footnote_definition';
-import FootnoteReference from '../extensions/footnote_reference';
-import Frontmatter from '../extensions/frontmatter';
-import HardBreak from '../extensions/hard_break';
-import Heading from '../extensions/heading';
-import HorizontalRule from '../extensions/horizontal_rule';
-import Highlight from '../extensions/highlight';
-import HTMLMarks from '../extensions/html_marks';
-import HTMLNodes from '../extensions/html_nodes';
-import Image from '../extensions/image';
-import InlineDiff from '../extensions/inline_diff';
-import Italic from '../extensions/italic';
-import Link from '../extensions/link';
-import ListItem from '../extensions/list_item';
-import Loading from '../extensions/loading';
-import MathInline from '../extensions/math_inline';
-import OrderedList from '../extensions/ordered_list';
-import Paragraph from '../extensions/paragraph';
-import Reference from '../extensions/reference';
-import ReferenceLabel from '../extensions/reference_label';
-import ReferenceDefinition from '../extensions/reference_definition';
-import Strike from '../extensions/strike';
-import Subscript from '../extensions/subscript';
-import Superscript from '../extensions/superscript';
-import Table from '../extensions/table';
-import TableCell from '../extensions/table_cell';
-import TableHeader from '../extensions/table_header';
-import TableOfContents from '../extensions/table_of_contents';
-import TableRow from '../extensions/table_row';
-import TaskItem from '../extensions/task_item';
-import TaskList from '../extensions/task_list';
-import Text from '../extensions/text';
-import Video from '../extensions/video';
-import WordBreak from '../extensions/word_break';
+import * as extensions from '../extensions';
 import {
   renderCodeBlock,
   renderHardBreak,
@@ -62,6 +13,8 @@ import {
   closeTag,
   renderOrderedList,
   renderImage,
+  renderHeading,
+  renderBlockquote,
   renderPlayable,
   renderHTMLNode,
   renderContent,
@@ -78,13 +31,13 @@ import {
 
 const defaultSerializerConfig = {
   marks: {
-    [Bold.name]: bold,
-    [Italic.name]: italic,
-    [Code.name]: code,
-    [Subscript.name]: { open: '<sub>', close: '</sub>', mixable: true },
-    [Superscript.name]: { open: '<sup>', close: '</sup>', mixable: true },
-    [Highlight.name]: { open: '<mark>', close: '</mark>', mixable: true },
-    [InlineDiff.name]: {
+    [extensions.Bold.name]: bold,
+    [extensions.Italic.name]: italic,
+    [extensions.Code.name]: code,
+    [extensions.Subscript.name]: { open: '<sub>', close: '</sub>', mixable: true },
+    [extensions.Superscript.name]: { open: '<sup>', close: '</sup>', mixable: true },
+    [extensions.Highlight.name]: { open: '<mark>', close: '</mark>', mixable: true },
+    [extensions.InlineDiff.name]: {
       mixable: true,
       open(_, mark) {
         return mark.attrs.type === 'addition' ? '{+' : '{-';
@@ -93,14 +46,14 @@ const defaultSerializerConfig = {
         return mark.attrs.type === 'addition' ? '+}' : '-}';
       },
     },
-    [Link.name]: link,
-    [MathInline.name]: {
+    [extensions.Link.name]: link,
+    [extensions.MathInline.name]: {
       open: (...args) => `$${defaultMarkdownSerializer.marks.code.open(...args)}`,
       close: (...args) => `${defaultMarkdownSerializer.marks.code.close(...args)}$`,
       escape: false,
     },
-    [Strike.name]: strike,
-    ...HTMLMarks.reduce(
+    [extensions.Strike.name]: strike,
+    ...extensions.HTMLMarks.reduce(
       (acc, { name }) => ({
         ...acc,
         [name]: {
@@ -116,38 +69,27 @@ const defaultSerializerConfig = {
   },
 
   nodes: {
-    [Audio.name]: preserveUnchanged({
+    [extensions.Audio.name]: preserveUnchanged({
       render: renderPlayable,
       inline: true,
     }),
-    [Blockquote.name]: preserveUnchanged((state, node) => {
-      if (node.attrs.multiline) {
-        state.write('>>>');
-        state.ensureNewLine();
-        state.renderContent(node);
-        state.ensureNewLine();
-        state.write('>>>');
-        state.closeBlock(node);
-      } else {
-        state.wrapBlock('> ', null, node, () => state.renderContent(node));
-      }
-    }),
-    [BulletList.name]: preserveUnchanged(renderBulletList),
-    [CodeBlockHighlight.name]: preserveUnchanged(renderCodeBlock),
-    [Diagram.name]: preserveUnchanged(renderCodeBlock),
-    [CodeSuggestion.name]: preserveUnchanged(renderCodeBlock),
-    [DrawioDiagram.name]: preserveUnchanged({
+    [extensions.Blockquote.name]: preserveUnchanged(renderBlockquote),
+    [extensions.BulletList.name]: preserveUnchanged(renderBulletList),
+    [extensions.CodeBlockHighlight.name]: preserveUnchanged(renderCodeBlock),
+    [extensions.Diagram.name]: preserveUnchanged(renderCodeBlock),
+    [extensions.CodeSuggestion.name]: preserveUnchanged(renderCodeBlock),
+    [extensions.DrawioDiagram.name]: preserveUnchanged({
       render: renderImage,
       inline: true,
     }),
-    [DescriptionList.name]: renderHTMLNode('dl', true),
-    [DescriptionItem.name]: (state, node, parent, index) => {
+    [extensions.DescriptionList.name]: renderHTMLNode('dl', true),
+    [extensions.DescriptionItem.name]: (state, node, parent, index) => {
       if (index === 1) state.ensureNewLine();
       renderHTMLNode(node.attrs.isTerm ? 'dt' : 'dd')(state, node);
       if (index === parent.childCount - 1) state.ensureNewLine();
     },
-    [Details.name]: renderHTMLNode('details', true),
-    [DetailsContent.name]: (state, node, parent, index) => {
+    [extensions.Details.name]: renderHTMLNode('details', true),
+    [extensions.DetailsContent.name]: (state, node, parent, index) => {
       if (!index) renderHTMLNode('summary')(state, node);
       else {
         if (index === 1) state.ensureNewLine();
@@ -155,23 +97,23 @@ const defaultSerializerConfig = {
         if (index === parent.childCount - 1) state.ensureNewLine();
       }
     },
-    [Emoji.name]: (state, node) => {
+    [extensions.Emoji.name]: (state, node) => {
       const { name } = node.attrs;
 
       state.write(`:${name}:`);
     },
-    [FootnoteDefinition.name]: preserveUnchanged((state, node) => {
+    [extensions.FootnoteDefinition.name]: preserveUnchanged((state, node) => {
       state.write(`[^${node.attrs.identifier}]: `);
       state.renderInline(node);
       state.ensureNewLine();
     }),
-    [FootnoteReference.name]: preserveUnchanged({
+    [extensions.FootnoteReference.name]: preserveUnchanged({
       render: (state, node) => {
         state.write(`[^${node.attrs.identifier}]`);
       },
       inline: true,
     }),
-    [Frontmatter.name]: preserveUnchanged((state, node) => {
+    [extensions.Frontmatter.name]: preserveUnchanged((state, node) => {
       const { language } = node.attrs;
       const syntax = {
         toml: '+++',
@@ -185,22 +127,24 @@ const defaultSerializerConfig = {
       state.write(syntax);
       state.closeBlock(node);
     }),
-    [Figure.name]: renderHTMLNode('figure'),
-    [FigureCaption.name]: renderHTMLNode('figcaption'),
-    [HardBreak.name]: preserveUnchanged(renderHardBreak),
-    [Heading.name]: preserveUnchanged(defaultMarkdownSerializer.nodes.heading),
-    [HorizontalRule.name]: preserveUnchanged(defaultMarkdownSerializer.nodes.horizontal_rule),
-    [Image.name]: preserveUnchanged({
+    [extensions.Figure.name]: renderHTMLNode('figure'),
+    [extensions.FigureCaption.name]: renderHTMLNode('figcaption'),
+    [extensions.HardBreak.name]: preserveUnchanged(renderHardBreak),
+    [extensions.Heading.name]: preserveUnchanged(renderHeading),
+    [extensions.HorizontalRule.name]: preserveUnchanged(
+      defaultMarkdownSerializer.nodes.horizontal_rule,
+    ),
+    [extensions.Image.name]: preserveUnchanged({
       render: renderImage,
       inline: true,
     }),
-    [ListItem.name]: preserveUnchanged(defaultMarkdownSerializer.nodes.list_item),
-    [Loading.name]: () => {},
-    [OrderedList.name]: preserveUnchanged(renderOrderedList),
-    [Paragraph.name]: preserveUnchanged(defaultMarkdownSerializer.nodes.paragraph),
-    [Reference.name]: renderReference,
-    [ReferenceLabel.name]: renderReferenceLabel,
-    [ReferenceDefinition.name]: preserveUnchanged({
+    [extensions.ListItem.name]: preserveUnchanged(defaultMarkdownSerializer.nodes.list_item),
+    [extensions.Loading.name]: () => {},
+    [extensions.OrderedList.name]: preserveUnchanged(renderOrderedList),
+    [extensions.Paragraph.name]: preserveUnchanged(defaultMarkdownSerializer.nodes.paragraph),
+    [extensions.Reference.name]: renderReference,
+    [extensions.ReferenceLabel.name]: renderReferenceLabel,
+    [extensions.ReferenceDefinition.name]: preserveUnchanged({
       render: (state, node, parent, index, same, sourceMarkdown) => {
         const nextSibling = parent.maybeChild(index + 1);
 
@@ -211,7 +155,7 @@ const defaultSerializerConfig = {
          * because it isn’t necessary and a more compact text format
          * is preferred.
          */
-        if (!nextSibling || nextSibling.type.name !== ReferenceDefinition.name) {
+        if (!nextSibling || nextSibling.type.name !== extensions.ReferenceDefinition.name) {
           state.closeBlock(node);
         } else {
           state.ensureNewLine();
@@ -219,34 +163,35 @@ const defaultSerializerConfig = {
       },
       overwriteSourcePreservationStrategy: true,
     }),
-    [TableOfContents.name]: preserveUnchanged((state, node) => {
+    [extensions.TableOfContents.name]: preserveUnchanged((state, node) => {
       state.write('[[_TOC_]]');
       state.closeBlock(node);
     }),
-    [Table.name]: preserveUnchanged(renderTable),
-    [TableCell.name]: renderTableCell,
-    [TableHeader.name]: renderTableCell,
-    [TableRow.name]: renderTableRow,
-    [TaskItem.name]: preserveUnchanged((state, node) => {
+    [extensions.Table.name]: preserveUnchanged(renderTable),
+    [extensions.TableCell.name]: renderTableCell,
+    [extensions.TableHeader.name]: renderTableCell,
+    [extensions.TableRow.name]: renderTableRow,
+    [extensions.TaskItem.name]: preserveUnchanged((state, node) => {
       let symbol = ' ';
       if (node.attrs.inapplicable) symbol = '~';
       else if (node.attrs.checked) symbol = 'x';
 
       state.write(`[${symbol}] `);
+
       if (!node.textContent) state.write('&nbsp;');
       state.renderContent(node);
     }),
-    [TaskList.name]: preserveUnchanged((state, node) => {
+    [extensions.TaskList.name]: preserveUnchanged((state, node) => {
       if (node.attrs.numeric) renderOrderedList(state, node);
       else renderBulletList(state, node);
     }),
-    [Text.name]: defaultMarkdownSerializer.nodes.text,
-    [Video.name]: preserveUnchanged({
+    [extensions.Text.name]: defaultMarkdownSerializer.nodes.text,
+    [extensions.Video.name]: preserveUnchanged({
       render: renderPlayable,
       inline: true,
     }),
-    [WordBreak.name]: (state) => state.write('<wbr>'),
-    ...HTMLNodes.reduce((serializers, htmlNode) => {
+    [extensions.WordBreak.name]: (state) => state.write('<wbr>'),
+    ...extensions.HTMLNodes.reduce((serializers, htmlNode) => {
       return {
         ...serializers,
         [htmlNode.name]: (state, node) => renderHTMLNode(htmlNode.options.tagName)(state, node),
@@ -310,7 +255,7 @@ export default class MarkdownSerializer {
    * changed.
    * @returns A String that represents the serialized document as Markdown
    */
-  serialize({ doc, pristineDoc }) {
+  serialize({ doc, pristineDoc }, { useCanonicalSrc = true, skipEmptyNodes = false } = {}) {
     const changeTracker = createChangeTracker(doc, pristineDoc);
     const serializer = new ProseMirrorMarkdownSerializer(
       {
@@ -325,6 +270,8 @@ export default class MarkdownSerializer {
 
     return serializer.serialize(doc, {
       tightLists: true,
+      useCanonicalSrc,
+      skipEmptyNodes,
       changeTracker,
       escapeExtraCharacters: /<|>/g,
     });
diff --git a/app/assets/javascripts/content_editor/services/serialization_helpers.js b/app/assets/javascripts/content_editor/services/serialization_helpers.js
index 7a2fbf8fcab..4bf61e34120 100644
--- a/app/assets/javascripts/content_editor/services/serialization_helpers.js
+++ b/app/assets/javascripts/content_editor/services/serialization_helpers.js
@@ -1,4 +1,5 @@
-import { uniq, isString, omit, isFunction } from 'lodash';
+import { uniq, omit, isFunction } from 'lodash';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 import { removeLastSlashInUrlPath, removeUrlProtocol } from '../../lib/utils/url_utility';
 
 const defaultAttrs = {
@@ -110,8 +111,8 @@ function htmlEncode(str = '') {
     .replace(/&/g, '&amp;')
     .replace(/</g, '&lt;')
     .replace(/>/g, '&gt;')
-    .replace(/'/g, '&#39;')
-    .replace(/"/g, '&#34;');
+    .replace(/'/g, '&apos;')
+    .replace(/"/g, '&quot;');
 }
 
 const shouldIgnoreAttr = (tagName, attrKey, attrValue) =>
@@ -337,15 +338,22 @@ export function renderHardBreak(state, node, parent, index) {
   }
 }
 
+function getMediaSrc(node, useCanonicalSrc = true) {
+  const { canonicalSrc, src } = node.attrs;
+
+  if (useCanonicalSrc) return canonicalSrc || src || '';
+  return src || '';
+}
+
 export function renderImage(state, node) {
-  const { alt, canonicalSrc, src, title, width, height, isReference } = node.attrs;
-  const realSrc = canonicalSrc || src || '';
+  const { alt, title, width, height, isReference } = node.attrs;
+  const realSrc = getMediaSrc(node, state.options.useCanonicalSrc);
   // eslint-disable-next-line @gitlab/require-i18n-strings
   if (realSrc.startsWith('data:') || realSrc.startsWith('blob:')) return;
 
-  if (isString(src) || isString(canonicalSrc)) {
+  if (realSrc) {
     const quotedTitle = title ? ` ${state.quote(title)}` : '';
-    const sourceExpression = isReference ? `[${canonicalSrc}]` : `(${realSrc}${quotedTitle})`;
+    const sourceExpression = isReference ? `[${realSrc}]` : `(${realSrc}${quotedTitle})`;
 
     const sizeAttributes = [];
     if (width) {
@@ -365,12 +373,44 @@ export function renderPlayable(state, node) {
   renderImage(state, node);
 }
 
+export function renderHeading(state, node) {
+  if (state.options.skipEmptyNodes && !node.childCount) return;
+
+  defaultMarkdownSerializer.nodes.heading(state, node);
+}
+
+export function renderBlockquote(state, node) {
+  if (state.options.skipEmptyNodes) {
+    if (!node.childCount) return;
+    if (node.childCount === 1) {
+      const child = node.child(0);
+      if (child.type.name === 'paragraph' && !child.childCount) return;
+    }
+  }
+
+  if (node.attrs.multiline) {
+    state.write('>>>');
+    state.ensureNewLine();
+    state.renderContent(node);
+    state.ensureNewLine();
+    state.write('>>>');
+    state.closeBlock(node);
+  } else {
+    state.wrapBlock('> ', null, node, () => state.renderContent(node));
+  }
+}
+
 export function renderCodeBlock(state, node) {
+  if (state.options.skipEmptyNodes && !node.childCount) return;
+
+  let { language } = node.attrs;
+  if (language === 'plaintext') language = '';
+
   const numBackticks = Math.max(2, node.textContent.match(/```+/g)?.[0]?.length || 0) + 1;
   const backticks = state.repeat('`', numBackticks);
   state.write(
     `${backticks}${
-      (node.attrs.language || '') + (node.attrs.langParams ? `:${node.attrs.langParams}` : '')
+      (language || '') + (node.attrs.langParams ? `:${node.attrs.langParams}` : '')
     }\n`,
   );
   state.text(node.textContent, false);
@@ -641,13 +681,20 @@ const isAutoLink = (linkMark, parent) => {
  */
 const isBracketAutoLink = (sourceMarkdown) => /^<.+?>$/.test(sourceMarkdown);
 
+function getLinkHref(mark, useCanonicalSrc = true) {
+  const { canonicalSrc, href } = mark.attrs;
+
+  if (useCanonicalSrc) return canonicalSrc || href || '';
+  return href || '';
+}
+
 export const link = {
   open(state, mark, parent) {
     if (isAutoLink(mark, parent)) {
       return isBracketAutoLink(mark.attrs.sourceMarkdown) ? '<' : '';
     }
 
-    const { canonicalSrc, href, title, sourceMarkdown } = mark.attrs;
+    const { href, title, sourceMarkdown } = mark.attrs;
 
     // eslint-disable-next-line @gitlab/require-i18n-strings
     if (href.startsWith('data:') || href.startsWith('blob:')) return '';
@@ -656,7 +703,9 @@ export const link = {
       return '[';
     }
 
-    const attrs = { href: state.esc(href || canonicalSrc || '') };
+    const attrs = {
+      href: state.esc(getLinkHref(mark, state.options.useCanonicalSrc)),
+    };
 
     if (title) {
       attrs.title = title;
@@ -669,25 +718,29 @@ export const link = {
       return isBracketAutoLink(mark.attrs.sourceMarkdown) ? '>' : '';
     }
 
-    const { canonicalSrc, href, title, sourceMarkdown, isReference } = mark.attrs;
+    const { href, title, sourceMarkdown, isReference } = mark.attrs;
 
     // eslint-disable-next-line @gitlab/require-i18n-strings
     if (href.startsWith('data:') || href.startsWith('blob:')) return '';
 
     if (isReference) {
-      return `][${state.esc(canonicalSrc || href || '')}]`;
+      return `][${state.esc(getLinkHref(mark, state.options.useCanonicalSrc))}]`;
     }
 
     if (linkType(sourceMarkdown) === LINK_HTML) {
       return closeTag('a');
     }
 
-    return `](${state.esc(canonicalSrc || href || '')}${title ? ` ${state.quote(title)}` : ''})`;
+    return `](${state.esc(getLinkHref(mark, state.options.useCanonicalSrc))}${
+      title ? ` ${state.quote(title)}` : ''
+    })`;
   },
 };
 
 const generateStrikeTag = (wrapTagName = openTag) => {
   return (_, mark) => {
+    if (mark.attrs.htmlTag) return wrapTagName(mark.attrs.htmlTag);
+
     const type = /^(~~|<del|<strike|<s).*/.exec(mark.attrs.sourceMarkdown)?.[1];
 
     switch (type) {
diff --git a/app/models/organizations/organization_setting.rb b/app/models/organizations/organization_setting.rb
index 108531e6701..fb141c164d3 100644
--- a/app/models/organizations/organization_setting.rb
+++ b/app/models/organizations/organization_setting.rb
@@ -2,6 +2,8 @@
 
 module Organizations
   class OrganizationSetting < ApplicationRecord
+    extend ::Organization::CurrentOrganization
+
     belongs_to :organization
 
     validates :settings, json_schema: { filename: "organization_settings" }
@@ -16,5 +18,11 @@ module Organizations
         end
       end
     end
+
+    def self.for_current_organization
+      return unless current_organization
+
+      current_organization.settings || current_organization.build_settings
+    end
   end
 end
diff --git a/glfm_specification/output_example_snapshots/prosemirror_json.yml b/glfm_specification/output_example_snapshots/prosemirror_json.yml
index ba2cbc8322c..34b8118cd78 100644
--- a/glfm_specification/output_example_snapshots/prosemirror_json.yml
+++ b/glfm_specification/output_example_snapshots/prosemirror_json.yml
@@ -3352,7 +3352,10 @@
             "type": "text",
             "marks": [
               {
-                "type": "strike"
+                "type": "strike",
+                "attrs": {
+                  "htmlTag": null
+                }
               }
             ],
             "text": "\n*foo*\n"
@@ -3375,7 +3378,10 @@
                 "type": "italic"
               },
               {
-                "type": "strike"
+                "type": "strike",
+                "attrs": {
+                  "htmlTag": null
+                }
               }
             ],
             "text": "foo"
@@ -3398,7 +3404,10 @@
                 "type": "italic"
               },
               {
-                "type": "strike"
+                "type": "strike",
+                "attrs": {
+                  "htmlTag": null
+                }
               }
             ],
             "text": "foo"
@@ -14842,7 +14851,10 @@
             "type": "text",
             "marks": [
               {
-                "type": "strike"
+                "type": "strike",
+                "attrs": {
+                  "htmlTag": null
+                }
               }
             ],
             "text": "Hi"
@@ -22303,7 +22315,10 @@
                     "type": "text",
                     "marks": [
                       {
-                        "type": "strike"
+                        "type": "strike",
+                        "attrs": {
+                          "htmlTag": null
+                        }
                       }
                     ],
                     "text": "great"
@@ -23125,7 +23140,10 @@
             "type": "text",
             "marks": [
               {
-                "type": "strike"
+                "type": "strike",
+                "attrs": {
+                  "htmlTag": null
+                }
               }
             ],
             "text": "del"
@@ -23267,7 +23285,10 @@
                         "type": "text",
                         "marks": [
                           {
-                            "type": "strike"
+                            "type": "strike",
+                            "attrs": {
+                              "htmlTag": null
+                            }
                           }
                         ],
                         "text": "strike"
@@ -23771,7 +23792,10 @@
                 }
               },
               {
-                "type": "strike"
+                "type": "strike",
+                "attrs": {
+                  "htmlTag": null
+                }
               }
             ],
             "text": "www.google.com"
@@ -23795,7 +23819,10 @@
                 }
               },
               {
-                "type": "strike"
+                "type": "strike",
+                "attrs": {
+                  "htmlTag": null
+                }
               }
             ],
             "text": "http://google.com"
diff --git a/lib/gitlab/current_settings.rb b/lib/gitlab/current_settings.rb
index 64e0478734b..a42b086319d 100644
--- a/lib/gitlab/current_settings.rb
+++ b/lib/gitlab/current_settings.rb
@@ -24,12 +24,18 @@ module Gitlab
         Gitlab::SafeRequestStore.delete(:current_application_settings)
       end
 
+      # rubocop:disable GitlabSecurity/PublicSend -- Method calls are forwarded to one of the setting classes
       def method_missing(name, *args, **kwargs, &block)
-        current_application_settings.send(name, *args, **kwargs, &block) # rubocop:disable GitlabSecurity/PublicSend
+        application_settings = current_application_settings
+
+        return application_settings.send(name, *args, **kwargs, &block) if application_settings.respond_to?(name)
+
+        Organizations::OrganizationSetting.for_current_organization.send(name, *args, **kwargs, &block)
       end
+      # rubocop:enable GitlabSecurity/PublicSend
 
       def respond_to_missing?(name, include_private = false)
-        current_application_settings.respond_to?(name, include_private) || super
+        current_application_settings.respond_to?(name, include_private) || Organizations::OrganizationSetting.for_current_organization.respond_to?(name, include_private) || super
       end
     end
   end
diff --git a/lib/gitlab/fake_application_settings.rb b/lib/gitlab/fake_application_settings.rb
index 0b9a4c161ae..da99d9b1b70 100644
--- a/lib/gitlab/fake_application_settings.rb
+++ b/lib/gitlab/fake_application_settings.rb
@@ -46,6 +46,10 @@ module Gitlab
     def method_missing(*)
       nil
     end
+
+    def respond_to_missing?(*)
+      true
+    end
   end
 end
 
diff --git a/locale/gitlab.pot b/locale/gitlab.pot
index e04e50bc347..e478817381d 100644
--- a/locale/gitlab.pot
+++ b/locale/gitlab.pot
@@ -48467,9 +48467,6 @@ msgstr ""
 msgid "TXT"
 msgstr ""
 
-msgid "Table of Contents"
-msgstr ""
-
 msgid "Table of contents"
 msgstr ""
 
diff --git a/spec/features/markdown/copy_as_gfm_spec.rb b/spec/features/markdown/copy_as_gfm_spec.rb
index 8073e7e9556..0f10da6ebad 100644
--- a/spec/features/markdown/copy_as_gfm_spec.rb
+++ b/spec/features/markdown/copy_as_gfm_spec.rb
@@ -29,7 +29,7 @@ RSpec.describe 'Copy as GFM', :js, feature_category: :team_planning do
     it 'transforms HTML to GFM', :aggregate_failures do
       verify(
         'nesting',
-        '> 1. [x] **[$`2 + 2`$ {-=-}{+=+} 2^2 ~~:thumbsup:~~](http://google.com)**'
+        '> 1. [x] [**$`2 + 2`$ {-=-}{+=+} 2^2 ~~:thumbsup:~~**](http://google.com)'
       )
 
       verify(
@@ -114,9 +114,9 @@ RSpec.describe 'Copy as GFM', :js, feature_category: :team_planning do
         GFM
         <<~GFM,
           1. [ ] Unchecked ordered task
-          1. [x] Checked ordered task
-          1. [~] Inapplicable ordered task
-          1. [~] Inapplicable ordered task with ~~del~~ and <s>strike</s> embedded
+          2. [x] Checked ordered task
+          3. [~] Inapplicable ordered task
+          4. [~] Inapplicable ordered task with ~~del~~ and <s>strike</s> embedded
         GFM
         <<~GFM
           * [ ] Unchecked loose list task
@@ -496,15 +496,14 @@ RSpec.describe 'Copy as GFM', :js, feature_category: :team_planning do
         <sub>sub</sub>
 
         <dl>
-          <dt>dt</dt>
-          <dt>dt</dt>
-          <dd>dd</dd>
-          <dd>dd</dd>
-
-          <dt>dt</dt>
-          <dt>dt</dt>
-          <dd>dd</dd>
-          <dd>dd</dd>
+        <dt>dt</dt>
+        <dt>dt</dt>
+        <dd>dd</dd>
+        <dd>dd</dd>
+        <dt>dt</dt>
+        <dt>dt</dt>
+        <dd>dd</dd>
+        <dd>dd</dd>
         </dl>
 
         <kbd>kbd</kbd>
@@ -518,9 +517,8 @@ RSpec.describe 'Copy as GFM', :js, feature_category: :team_planning do
         <abbr title="HyperText &quot;Markup&quot; Language">HTML</abbr>
 
         <details>
-        <summary>summary></summary>
-
-        details
+        <summary>summary</summary>
+         details
         </details>
         GFM
       )
@@ -542,17 +540,20 @@ RSpec.describe 'Copy as GFM', :js, feature_category: :team_planning do
         <<~GFM
           Foo
 
-              ```js
-              Code goes here
-              ```
+          ````
+          ```js
+          Code goes here
+          ```
+          ````
         GFM
       )
 
       verify(
         'MarkdownFilter',
-        "Line with two spaces at the end  \nto insert a linebreak",
+        "Line with backslash at the end\\\nto insert a linebreak",
         '`code`',
-        '`` code with ` ticks ``',
+        '``code with ` ticks``',
+        '`` `nested` code ``',
         '> Quote',
         # multiline quote
         <<~GFM,
@@ -589,7 +590,7 @@ RSpec.describe 'Copy as GFM', :js, feature_category: :team_planning do
         GFM
         <<~GFM,
           1. Ordered list item
-          1. Ordered list item 2
+          2. Ordered list item 2
         GFM
 
         # multiline ordered list item
@@ -618,7 +619,7 @@ RSpec.describe 'Copy as GFM', :js, feature_category: :team_planning do
         '##### Heading',
         '###### Heading',
         '**Bold**',
-        '*Italics*',
+        '_Italics_',
         '~~Strikethrough (del)~~',
         '<s>Strikethrough</s>',
         '---',
diff --git a/spec/frontend/behaviors/copy_as_gfm_spec.js b/spec/frontend/behaviors/copy_as_gfm_spec.js
index 2032faa1c33..a35cf2f0b13 100644
--- a/spec/frontend/behaviors/copy_as_gfm_spec.js
+++ b/spec/frontend/behaviors/copy_as_gfm_spec.js
@@ -1,6 +1,8 @@
 import waitForPromises from 'helpers/wait_for_promises';
 import initCopyAsGFM, { CopyAsGFM } from '~/behaviors/markdown/copy_as_gfm';
 
+jest.mock('~/emoji');
+
 describe('CopyAsGFM', () => {
   describe('CopyAsGFM.pasteGFM', () => {
     let target;
@@ -116,7 +118,7 @@ describe('CopyAsGFM', () => {
         window.getSelection = jest.fn(() => selection);
         await simulateCopy();
 
-        const expectedGFM = '1. List Item1\n1. List Item2';
+        const expectedGFM = '1. List Item1\n2. List Item2';
 
         expect(clipboardData.setData).toHaveBeenCalledWith('text/x-gfm', expectedGFM);
       });
diff --git a/spec/frontend/behaviors/shortcuts/shortcuts_issuable_spec.js b/spec/frontend/behaviors/shortcuts/shortcuts_issuable_spec.js
index 6db99e796d6..3951714c64e 100644
--- a/spec/frontend/behaviors/shortcuts/shortcuts_issuable_spec.js
+++ b/spec/frontend/behaviors/shortcuts/shortcuts_issuable_spec.js
@@ -11,6 +11,8 @@ jest.mock('~/lib/utils/common_utils', () => ({
   getSelectedFragment: jest.fn().mockName('getSelectedFragment'),
 }));
 
+jest.mock('~/emoji');
+
 describe('ShortcutsIssuable', () => {
   beforeAll(() => {
     initCopyAsGFM();
@@ -215,7 +217,7 @@ describe('ShortcutsIssuable', () => {
         ShortcutsIssuable.replyWithSelectedText(true);
 
         await waitForPromises();
-        expect($(FORM_SELECTOR).val()).toBe('> *Selected text.*\n\n');
+        expect($(FORM_SELECTOR).val()).toBe('> _Selected text._\n\n');
       });
 
       it('triggers `focus`', async () => {
diff --git a/spec/frontend/content_editor/extensions/code_suggestion_spec.js b/spec/frontend/content_editor/extensions/code_suggestion_spec.js
index 86656fb96c3..b513735af22 100644
--- a/spec/frontend/content_editor/extensions/code_suggestion_spec.js
+++ b/spec/frontend/content_editor/extensions/code_suggestion_spec.js
@@ -28,7 +28,7 @@ describe('content_editor/extensions/code_suggestion', () => {
   let doc;
   let codeSuggestion;
 
-  const codeSuggestionConfig = {
+  const codeSuggestionsConfig = {
     canSuggest: true,
     line: { new_line: 5 },
     lines: [{ new_line: 5 }],
@@ -43,7 +43,9 @@ describe('content_editor/extensions/code_suggestion', () => {
     tiptapEditor = createTestEditor({
       extensions: [
         CodeBlockHighlight,
-        CodeSuggestion.configure({ config: { ...codeSuggestionConfig, ...config } }),
+        CodeSuggestion.configure({
+          codeSuggestionsConfig: { ...codeSuggestionsConfig, ...config },
+        }),
       ],
     });
 
diff --git a/spec/frontend/content_editor/services/markdown_serializer_spec.js b/spec/frontend/content_editor/services/markdown_serializer_spec.js
index 4ae39f7a5a7..aeaa63a332f 100644
--- a/spec/frontend/content_editor/services/markdown_serializer_spec.js
+++ b/spec/frontend/content_editor/services/markdown_serializer_spec.js
@@ -138,10 +138,10 @@ const {
   },
 });
 
-const serialize = (...content) =>
-  new MarkdownSerializer().serialize({
-    doc: doc(...content),
-  });
+const serializeWithOptions = (options, ...content) =>
+  new MarkdownSerializer().serialize({ doc: doc(...content) }, options);
+
+const serialize = (...content) => new MarkdownSerializer().serialize({ doc: doc(...content) });
 
 describe('markdownSerializer', () => {
   it('correctly serializes bold', () => {
@@ -389,6 +389,16 @@ describe('markdownSerializer', () => {
     expect(serialize(paragraph(strike('deleted content')))).toBe('~~deleted content~~');
   });
 
+  it.each`
+    strikeTag
+    ${'s'}
+    ${'strike'}
+  `('correctly serializes strikethrough with "$strikeTag" tag', ({ strikeTag }) => {
+    expect(serialize(paragraph(strike({ htmlTag: strikeTag }, 'deleted content')))).toBe(
+      `<${strikeTag}>deleted content</${strikeTag}>`,
+    );
+  });
+
   it('correctly serializes blockquotes with hard breaks', () => {
     expect(serialize(blockquote('some text', hardBreak(), hardBreak(), 'new line'))).toBe(
       `
@@ -411,6 +421,32 @@ describe('markdownSerializer', () => {
     );
   });
 
+  it('correctly serializes a blockquote with a nested blockquote', () => {
+    expect(
+      serialize(
+        blockquote(
+          paragraph('some paragraph'),
+          blockquote(paragraph('nested paragraph'), codeBlock('var x = 10;')),
+        ),
+      ),
+    ).toBe(
+      `
+> some paragraph
+>
+> > nested paragraph
+> >
+> > \`\`\`
+> > var x = 10;
+> > \`\`\`
+      `.trim(),
+    );
+  });
+
+  it('skips serializing an empty blockquote if skipEmptyNodes=true', () => {
+    expect(serializeWithOptions({ skipEmptyNodes: true }, blockquote())).toBe('');
+    expect(serializeWithOptions({ skipEmptyNodes: true }, blockquote(paragraph()))).toBe('');
+  });
+
   it('correctly serializes a multiline blockquote', () => {
     expect(
       serialize(
@@ -451,6 +487,23 @@ this is not really json but just trying out whether this case works or not
     );
   });
 
+  it('renders a plaintext code block without a prefix', () => {
+    expect(
+      serialize(
+        codeBlock(
+          { language: 'plaintext', langParams: '' },
+          'this is not really json but just trying out whether this case works or not',
+        ),
+      ),
+    ).toBe(
+      `
+\`\`\`
+this is not really json but just trying out whether this case works or not
+\`\`\`
+      `.trim(),
+    );
+  });
+
   it('correctly serializes a code block with language parameters', () => {
     expect(
       serialize(
@@ -514,6 +567,10 @@ var a = 0;
     );
   });
 
+  it('skips serializing an empty code block if skipEmptyNodes=true', () => {
+    expect(serializeWithOptions({ skipEmptyNodes: true }, codeBlock())).toBe('');
+  });
+
   it('correctly serializes emoji', () => {
     expect(serialize(paragraph(emoji({ name: 'dog' })))).toBe(':dog:');
   });
@@ -545,6 +602,20 @@ var a = 0;
     );
   });
 
+  it('skips serializing an empty heading if skipEmptyNodes=true', () => {
+    expect(
+      serializeWithOptions(
+        { skipEmptyNodes: true },
+        heading({ level: 1 }),
+        heading({ level: 2 }),
+        heading({ level: 3 }),
+        heading({ level: 4 }),
+        heading({ level: 5 }),
+        heading({ level: 6 }),
+      ),
+    ).toBe('');
+  });
+
   it('correctly serializes horizontal rule', () => {
     expect(serialize(horizontalRule(), horizontalRule(), horizontalRule())).toBe(
       `
@@ -614,6 +685,22 @@ var a = 0;
     ).toBe('![this is an image](file.png "foo bar baz")');
   });
 
+  it('does not use the canonicalSrc if options.useCanonicalSrc=false', () => {
+    expect(
+      serializeWithOptions(
+        { useCanonicalSrc: false },
+        paragraph(
+          image({
+            src: '/uploads/abcde/file.png',
+            alt: 'this is an image',
+            canonicalSrc: 'file.png',
+            title: 'foo bar baz',
+          }),
+        ),
+      ),
+    ).toBe('![this is an image](/uploads/abcde/file.png "foo bar baz")');
+  });
+
   it('correctly serializes bullet list', () => {
     expect(
       serialize(
diff --git a/spec/lib/gitlab/current_settings_spec.rb b/spec/lib/gitlab/current_settings_spec.rb
index 7fc50438c95..17b2218e05c 100644
--- a/spec/lib/gitlab/current_settings_spec.rb
+++ b/spec/lib/gitlab/current_settings_spec.rb
@@ -88,6 +88,8 @@ RSpec.describe Gitlab::CurrentSettings, feature_category: :shared do
   end
 
   describe '#current_application_settings', :use_clean_rails_memory_store_caching do
+    let_it_be(:organization_settings) { create(:organization_setting, restricted_visibility_levels: [Gitlab::VisibilityLevel::INTERNAL]) }
+
     it 'allows keys to be called directly' do
       described_class.update!(home_page_url: 'http://mydomain.com', signup_enabled: false)
 
@@ -97,10 +99,58 @@ RSpec.describe Gitlab::CurrentSettings, feature_category: :shared do
       expect(described_class.metrics_sample_interval).to be(15)
     end
 
-    it 'retrieves settings using ApplicationSettingFetcher' do
-      expect(Gitlab::ApplicationSettingFetcher).to receive(:current_application_settings).and_call_original
+    context 'when key is in ApplicationSettingFetcher' do
+      it 'retrieves settings using ApplicationSettingFetcher' do
+        expect(Gitlab::ApplicationSettingFetcher).to receive(:current_application_settings).and_call_original
+
+        described_class.home_page_url
+      end
+    end
+
+    context 'when key is in OrganizationSetting' do
+      before do
+        allow(Gitlab::ApplicationSettingFetcher).to receive(:current_application_settings).and_return(nil)
+      end
+
+      context 'and the current organization is known' do
+        before do
+          allow(Organizations::OrganizationSetting).to receive(:for_current_organization).and_return(organization_settings)
+        end
+
+        it 'retrieves settings using OrganizationSetting' do
+          expect(described_class.restricted_visibility_levels).to eq(organization_settings.restricted_visibility_levels)
+        end
+      end
+
+      context 'and the current organization is unknown' do
+        before do
+          allow(Organizations::OrganizationSetting).to receive(:for_current_organization).and_return(nil)
+        end
+
+        it 'raises NoMethodError' do
+          expect { described_class.foo }.to raise_error(NoMethodError)
+        end
+      end
+    end
+
+    context 'when key is in both sources' do
+      it 'for test purposes, ensure the values are different' do
+        expect(
+          Gitlab::ApplicationSettingFetcher.current_application_settings.restricted_visibility_levels
+        ).not_to eq(organization_settings.restricted_visibility_levels)
+      end
 
-      described_class.home_page_url
+      it 'prefers ApplicationSettingFetcher' do
+        expect(described_class.restricted_visibility_levels).to eq(
+          Gitlab::ApplicationSettingFetcher.current_application_settings.restricted_visibility_levels
+        )
+      end
+    end
+
+    context 'when key is in neither' do
+      it 'raises NoMethodError' do
+        expect { described_class.foo }.to raise_error(NoMethodError)
+      end
     end
   end
 
diff --git a/spec/models/organizations/organization_setting_spec.rb b/spec/models/organizations/organization_setting_spec.rb
index 376d0b7fe77..dd90a4d0f58 100644
--- a/spec/models/organizations/organization_setting_spec.rb
+++ b/spec/models/organizations/organization_setting_spec.rb
@@ -4,6 +4,7 @@ require 'spec_helper'
 
 RSpec.describe Organizations::OrganizationSetting, type: :model, feature_category: :cell do
   let_it_be(:organization) { create(:organization) }
+  let_it_be(:organization_setting) { create(:organization_setting, organization: organization) }
 
   describe 'associations' do
     it { is_expected.to belong_to :organization }
@@ -54,4 +55,41 @@ RSpec.describe Organizations::OrganizationSetting, type: :model, feature_categor
       end
     end
   end
+
+  describe '.for_current_organization' do
+    let(:dummy_class) { Class.new { extend Organization::CurrentOrganization } }
+
+    subject(:settings) { described_class.for_current_organization }
+
+    context 'when there is no current organization' do
+      it { is_expected.to be_nil }
+    end
+
+    context 'when there is a current organization' do
+      before do
+        dummy_class.current_organization = organization
+      end
+
+      after do
+        dummy_class.current_organization = nil
+      end
+
+      it 'returns current organization' do
+        expect(settings).to eq(organization_setting)
+      end
+
+      context 'when current organization does not have settings' do
+        before do
+          allow(organization).to receive(:settings).and_return(nil)
+        end
+
+        it 'returns new settings record' do
+          new_settings = settings
+
+          expect(new_settings.organization).to eq(organization)
+          expect(new_settings.new_record?).to eq(true)
+        end
+      end
+    end
+  end
 end
diff --git a/spec/scripts/lib/glfm/update_example_snapshots_spec.rb b/spec/scripts/lib/glfm/update_example_snapshots_spec.rb
index 4897dbea09c..78cdb81f80c 100644
--- a/spec/scripts/lib/glfm/update_example_snapshots_spec.rb
+++ b/spec/scripts/lib/glfm/update_example_snapshots_spec.rb
@@ -746,7 +746,10 @@ RSpec.describe Glfm::UpdateExampleSnapshots, '#process', feature_category: :team
                       "type": "text",
                       "marks": [
                         {
-                          "type": "strike"
+                          "type": "strike",
+                          "attrs": {
+                            "htmlTag": null
+                          }
                         }
                       ],
                       "text": "Hi"