diff --git a/package.json b/package.json
index c6adf6b..c78a6d5 100644
--- a/package.json
+++ b/package.json
@@ -136,6 +136,7 @@
     "remark-comment-config": "^8.0.0",
     "remark-gfm": "^4.0.0",
     "remark-github": "^12.0.0",
+    "remark-mdx": "^3.0.0",
     "remark-toc": "^9.0.0",
     "remark-validate-links": "^13.0.0",
     "strip-indent": "^4.0.0",
diff --git a/packages/remark-lint-checkbox-character-style/index.js b/packages/remark-lint-checkbox-character-style/index.js
index 62bfa98..7cc101a 100644
--- a/packages/remark-lint-checkbox-character-style/index.js
+++ b/packages/remark-lint-checkbox-character-style/index.js
@@ -206,8 +206,8 @@ const remarkLintCheckboxCharacterStyle = lintRule(
         value.slice(point.offset - 2, point.offset + 1)
       )
 
-      // Failsafe to make sure we don‘t crash if there actually isn’t a checkbox.
-      /* c8 ignore next */
+      /* c8 ignore next 2 -- failsafe so we don’t crash if there actually isn’t
+       * a checkbox. */
       if (!match) return
 
       const style = node.checked ? checked : unchecked
diff --git a/packages/remark-lint-checkbox-character-style/readme.md b/packages/remark-lint-checkbox-character-style/readme.md
index 5be4c79..35b519c 100644
--- a/packages/remark-lint-checkbox-character-style/readme.md
+++ b/packages/remark-lint-checkbox-character-style/readme.md
@@ -182,7 +182,8 @@ When configured with `{ checked: 'x' }`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 - [x] List item
@@ -199,7 +200,8 @@ When configured with `{ checked: 'X' }`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 - [X] List item
@@ -216,7 +218,8 @@ When configured with `{ unchecked: ' ' }`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 - [ ] List item
@@ -235,7 +238,8 @@ When configured with `{ unchecked: '\t' }`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 - [␉] List item
@@ -250,7 +254,8 @@ No messages.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 - [x] List item
diff --git a/packages/remark-lint-checkbox-content-indent/readme.md b/packages/remark-lint-checkbox-content-indent/readme.md
index a597fd2..b21309e 100644
--- a/packages/remark-lint-checkbox-content-indent/readme.md
+++ b/packages/remark-lint-checkbox-content-indent/readme.md
@@ -159,7 +159,8 @@ content after them with a single space between.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 - [ ] List item
@@ -176,7 +177,8 @@ No messages.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 - [ ] List item
diff --git a/packages/remark-lint-final-definition/index.js b/packages/remark-lint-final-definition/index.js
index bbefd95..c4812b2 100644
--- a/packages/remark-lint-final-definition/index.js
+++ b/packages/remark-lint-final-definition/index.js
@@ -57,26 +57,44 @@
  * @example
  *   {"name": "not-ok.md", "label": "output"}
  *
- *   3:1-3:47: Move definitions to the end of the file (after the node at line `5`)
+ *   3:1-3:47: Move definitions to the end of the file (after `5:19`)
  *
  * @example
- *   {"name": "ok-comments.md"}
+ *   {"name": "ok-html-comments.md"}
  *
  *   Paragraph.
  *
  *   [example-1]: http://example.com/one/
  *
- *   <!-- Comments are fine between and after definitions -->
+ *   <!-- Comments are fine between and after definitions. -->
+ *
+ *   [example-2]: http://example.com/two/
+ *
+ * @example
+ *   {"name": "ok-mdx-comments.mdx", "mdx": true}
+ *
+ *   Paragraph.
+ *
+ *   [example-1]: http://example.com/one/
+ *
+ *   {/* Comments are fine in MDX. *␀/}
  *
  *   [example-2]: http://example.com/two/
  */
 
 /**
+ * @typedef {import('mdast').Definition} Definition
+ * @typedef {import('mdast').FootnoteDefinition} FootnoteDefinition
  * @typedef {import('mdast').Root} Root
+ *
+ * @typedef {import('unist').Point} Point
  */
 
+/// <reference types="mdast-util-mdx" />
+
 import {lintRule} from 'unified-lint-rule'
-import {pointStart} from 'unist-util-position'
+import {pointEnd, pointStart} from 'unist-util-position'
+import {stringifyPosition} from 'unist-util-stringify-position'
 import {visit} from 'unist-util-visit'
 
 const remarkLintFinalDefinition = lintRule(
@@ -91,40 +109,47 @@ const remarkLintFinalDefinition = lintRule(
    *   Nothing.
    */
   function (tree, file) {
-    let last = 0
+    /** @type {Array<Definition | FootnoteDefinition>} */
+    const definitions = []
+    /** @type {Point | undefined} */
+    let last
 
-    visit(
-      tree,
-      function (node) {
-        const start = pointStart(node)
+    visit(tree, function (node) {
+      if (node.type === 'definition' || node.type === 'footnoteDefinition') {
+        definitions.push(node)
+      } else if (
+        node.type === 'root' ||
+        node.type === 'blockquote' ||
+        node.type === 'listItem' ||
+        // Ignore HTML comments.
+        (node.type === 'html' && /^[\t ]*<!--/.test(node.value)) ||
+        // Ignore MDX comments.
+        ((node.type === 'mdxFlowExpression' ||
+          node.type === 'mdxTextExpression') &&
+          /^\s*\/\*/.test(node.value))
+      ) {
+        // Empty.
+      } else {
+        const place = pointEnd(node)
 
-        // To do: ignore MDX comments?
-        // Ignore generated and HTML comment nodes.
-        if (
-          !start ||
-          node.type === 'root' ||
-          (node.type === 'html' && /^\s*<!--/.test(node.value))
-        ) {
-          return
+        if (place) {
+          last = place
         }
+      }
+    })
 
-        const line = start.line
+    for (const node of definitions) {
+      const point = pointStart(node)
 
-        if (node.type === 'definition') {
-          if (last && last > line) {
-            file.message(
-              'Move definitions to the end of the file (after the node at line `' +
-                last +
-                '`)',
-              node
-            )
-          }
-        } else if (last === 0) {
-          last = line
-        }
-      },
-      true
-    )
+      if (point && last && point.line < last.line) {
+        file.message(
+          'Move definitions to the end of the file (after `' +
+            stringifyPosition(last) +
+            '`)',
+          node
+        )
+      }
+    }
   }
 )
 
diff --git a/packages/remark-lint-final-definition/package.json b/packages/remark-lint-final-definition/package.json
index 6e46081..77c964f 100644
--- a/packages/remark-lint-final-definition/package.json
+++ b/packages/remark-lint-final-definition/package.json
@@ -33,8 +33,11 @@
   ],
   "dependencies": {
     "@types/mdast": "^4.0.0",
+    "@types/unist": "^3.0.0",
+    "mdast-util-mdx": "^3.0.0",
     "unified-lint-rule": "^2.0.0",
     "unist-util-position": "^5.0.0",
+    "unist-util-stringify-position": "^4.0.0",
     "unist-util-visit": "^5.0.0"
   },
   "scripts": {},
diff --git a/packages/remark-lint-final-definition/readme.md b/packages/remark-lint-final-definition/readme.md
index 93a88d2..3f3c300 100644
--- a/packages/remark-lint-final-definition/readme.md
+++ b/packages/remark-lint-final-definition/readme.md
@@ -171,10 +171,10 @@ Another paragraph.
 ###### Out
 
 ```text
-3:1-3:47: Move definitions to the end of the file (after the node at line `5`)
+3:1-3:47: Move definitions to the end of the file (after `5:19`)
 ```
 
-##### `ok-comments.md`
+##### `ok-html-comments.md`
 
 ###### In
 
@@ -183,7 +183,28 @@ Paragraph.
 
 [example-1]: http://example.com/one/
 
-<!-- Comments are fine between and after definitions -->
+<!-- Comments are fine between and after definitions. -->
+
+[example-2]: http://example.com/two/
+```
+
+###### Out
+
+No messages.
+
+##### `ok-mdx-comments.mdx`
+
+###### In
+
+> 👉 **Note**: this example uses
+> MDX ([`remark-mdx`][github-remark-mdx]).
+
+```mdx
+Paragraph.
+
+[example-1]: http://example.com/one/
+
+{/* Comments are fine in MDX. */}
 
 [example-2]: http://example.com/two/
 ```
@@ -263,6 +284,8 @@ abide by its terms.
 
 [github-remark-lint]: https://github.com/remarkjs/remark-lint
 
+[github-remark-mdx]: https://mdxjs.com/packages/remark-mdx/
+
 [github-unified-transformer]: https://github.com/unifiedjs/unified#transformer
 
 [npm-install]: https://docs.npmjs.com/cli/install
diff --git a/packages/remark-lint-final-newline/index.js b/packages/remark-lint-final-newline/index.js
index 60343ce..bad9635 100644
--- a/packages/remark-lint-final-newline/index.js
+++ b/packages/remark-lint-final-newline/index.js
@@ -81,6 +81,7 @@
  */
 
 import {lintRule} from 'unified-lint-rule'
+import {location} from 'vfile-location'
 
 const remarkLintFinalNewline = lintRule(
   {
@@ -95,11 +96,11 @@ const remarkLintFinalNewline = lintRule(
    */
   function (_, file) {
     const value = String(file)
+    const end = location(file).toPoint(value.length)
     const last = value.length - 1
 
-    if (last > -1 && value.charAt(last) !== '\n') {
-      // To do: warn at last character.
-      file.message('Missing newline character at end of file')
+    if (end && last > -1 && value.charAt(last) !== '\n') {
+      file.message('Missing newline character at end of file', end)
     }
   }
 )
diff --git a/packages/remark-lint-final-newline/package.json b/packages/remark-lint-final-newline/package.json
index dd316fc..52f26dc 100644
--- a/packages/remark-lint-final-newline/package.json
+++ b/packages/remark-lint-final-newline/package.json
@@ -33,7 +33,8 @@
   ],
   "dependencies": {
     "@types/mdast": "^4.0.0",
-    "unified-lint-rule": "^2.0.0"
+    "unified-lint-rule": "^2.0.0",
+    "vfile-location": "^5.0.0"
   },
   "scripts": {},
   "typeCoverage": {
diff --git a/packages/remark-lint-first-heading-level/index.js b/packages/remark-lint-first-heading-level/index.js
index f37338b..86835d3 100644
--- a/packages/remark-lint-first-heading-level/index.js
+++ b/packages/remark-lint-first-heading-level/index.js
@@ -143,6 +143,13 @@
  *   {"name": "not-ok-html.md", "config": 2, "label": "output"}
  *
  *   1:1-1:14: First heading level should be `2`
+ *
+ * @example
+ *   {"name": "ok.mdx", "mdx": true}
+ *
+ *   In <b>MDX</b>, JSX is supported.
+ *
+ *   <h1>First heading</h1>
  */
 
 /**
@@ -158,11 +165,14 @@
  *   Configuration.
  */
 
+/// <reference types="mdast-util-mdx" />
+
 import {lintRule} from 'unified-lint-rule'
 import {position} from 'unist-util-position'
 import {EXIT, visit} from 'unist-util-visit'
 
-const re = /<h([1-6])/
+const htmlRe = /<h([1-6])/
+const jsxNameRe = /h([1-6])/
 
 const remarkLintFirstHeadingLevel = lintRule(
   {
@@ -187,11 +197,17 @@ const remarkLintFirstHeadingLevel = lintRule(
         /** @type {Depth | undefined} */
         let rank
 
-        // To do: MDX?
         if (node.type === 'heading') {
           rank = node.depth
         } else if (node.type === 'html') {
-          const results = node.value.match(re)
+          const results = node.value.match(htmlRe)
+          rank = results ? /** @type {Depth} */ (Number(results[1])) : undefined
+        } else if (
+          (node.type === 'mdxJsxFlowElement' ||
+            node.type === 'mdxJsxTextElement') &&
+          node.name
+        ) {
+          const results = node.name.match(jsxNameRe)
           rank = results ? /** @type {Depth} */ (Number(results[1])) : undefined
         }
 
diff --git a/packages/remark-lint-first-heading-level/package.json b/packages/remark-lint-first-heading-level/package.json
index 6845210..d113d4b 100644
--- a/packages/remark-lint-first-heading-level/package.json
+++ b/packages/remark-lint-first-heading-level/package.json
@@ -34,6 +34,7 @@
   ],
   "dependencies": {
     "@types/mdast": "^4.0.0",
+    "mdast-util-mdx": "^3.0.0",
     "unified-lint-rule": "^2.0.0",
     "unist-util-position": "^5.0.0",
     "unist-util-visit": "^5.0.0"
diff --git a/packages/remark-lint-first-heading-level/readme.md b/packages/remark-lint-first-heading-level/readme.md
index bccedd0..a0a4c0c 100644
--- a/packages/remark-lint-first-heading-level/readme.md
+++ b/packages/remark-lint-first-heading-level/readme.md
@@ -305,6 +305,23 @@ Paragraph.
 1:1-1:14: First heading level should be `2`
 ```
 
+##### `ok.mdx`
+
+###### In
+
+> 👉 **Note**: this example uses
+> MDX ([`remark-mdx`][github-remark-mdx]).
+
+```mdx
+In <b>MDX</b>, JSX is supported.
+
+<h1>First heading</h1>
+```
+
+###### Out
+
+No messages.
+
 ## Compatibility
 
 Projects maintained by the unified collective are compatible with maintained
@@ -380,6 +397,8 @@ abide by its terms.
 
 [github-remark-lint]: https://github.com/remarkjs/remark-lint
 
+[github-remark-mdx]: https://mdxjs.com/packages/remark-mdx/
+
 [github-unified-transformer]: https://github.com/unifiedjs/unified#transformer
 
 [npm-install]: https://docs.npmjs.com/cli/install
diff --git a/packages/remark-lint-list-item-content-indent/index.js b/packages/remark-lint-list-item-content-indent/index.js
index 4d7c2b2..2eacaa0 100644
--- a/packages/remark-lint-list-item-content-indent/index.js
+++ b/packages/remark-lint-list-item-content-indent/index.js
@@ -126,8 +126,7 @@ const remarkLintListItemContentIndent = lintRule(
 
           file.message(
             'Don’t use mixed indentation for children, ' +
-              // Hard to test, I couldn’t find it at least.
-              /* c8 ignore next */
+              /* c8 ignore next -- hard to test, I couldn’t find it at least. */
               (diff > 0 ? 'add' : 'remove') +
               ' ' +
               abs +
diff --git a/packages/remark-lint-list-item-content-indent/readme.md b/packages/remark-lint-list-item-content-indent/readme.md
index cbc9a48..7df9258 100644
--- a/packages/remark-lint-list-item-content-indent/readme.md
+++ b/packages/remark-lint-list-item-content-indent/readme.md
@@ -151,7 +151,8 @@ Further children should align with it.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 1.␠[x] Alpha
@@ -166,7 +167,8 @@ No messages.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 1.␠[x] Charlie
diff --git a/packages/remark-lint-maximum-line-length/index.js b/packages/remark-lint-maximum-line-length/index.js
index 9432d6f..18e14fb 100644
--- a/packages/remark-lint-maximum-line-length/index.js
+++ b/packages/remark-lint-maximum-line-length/index.js
@@ -119,6 +119,8 @@
  *   4:12: Line must be at most 10 characters
  */
 
+/// <reference types="mdast-util-mdx" />
+
 /**
  * @typedef {import('mdast').Root} Root
  */
@@ -146,26 +148,14 @@ const remarkLintMaximumLineLength = lintRule(
     const option = options || 80
 
     visit(tree, function (node) {
-      // To do: add MDX types, etc.
-      // To do: remove MDX 1?
       if (
         node.type === 'code' ||
         node.type === 'definition' ||
         node.type === 'heading' ||
         node.type === 'html' ||
-        node.type === 'table' ||
-        // @ts-expect-error: These are from MDX@1 and MDX@2: <https://github.com/mdx-js/specification>.
-        node.type === 'jsx' ||
-        // @ts-expect-error: MDX
-        node.type === 'mdxFlowExpression' ||
-        // @ts-expect-error: MDX
-        node.type === 'mdxJsxFlowElement' ||
-        // @ts-expect-error: MDX
         node.type === 'mdxJsxTextElement' ||
-        // @ts-expect-error: MDX
         node.type === 'mdxTextExpression' ||
-        // @ts-expect-error: MDX
-        node.type === 'mdxjsEsm' ||
+        node.type === 'table' ||
         // @ts-expect-error: TOML from frontmatter.
         node.type === 'toml' ||
         node.type === 'yaml'
diff --git a/packages/remark-lint-maximum-line-length/package.json b/packages/remark-lint-maximum-line-length/package.json
index 9fa6008..cf95306 100644
--- a/packages/remark-lint-maximum-line-length/package.json
+++ b/packages/remark-lint-maximum-line-length/package.json
@@ -32,6 +32,7 @@
   ],
   "dependencies": {
     "@types/mdast": "^4.0.0",
+    "mdast-util-mdx": "^3.0.0",
     "unified-lint-rule": "^2.0.0",
     "unist-util-position": "^5.0.0",
     "unist-util-visit": "^5.0.0"
diff --git a/packages/remark-lint-maximum-line-length/readme.md b/packages/remark-lint-maximum-line-length/readme.md
index a6b2907..f04ec3b 100644
--- a/packages/remark-lint-maximum-line-length/readme.md
+++ b/packages/remark-lint-maximum-line-length/readme.md
@@ -151,7 +151,8 @@ Whether to wrap prose or not is a stylistic choice.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 This line is simply not toooooooooooooooooooooooooooooooooooooooooooo
diff --git a/packages/remark-lint-no-literal-urls/readme.md b/packages/remark-lint-no-literal-urls/readme.md
index fa06a25..c42aaa9 100644
--- a/packages/remark-lint-no-literal-urls/readme.md
+++ b/packages/remark-lint-no-literal-urls/readme.md
@@ -166,7 +166,8 @@ No messages.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 http://foo.bar/baz
diff --git a/packages/remark-lint-no-shell-dollars/index.js b/packages/remark-lint-no-shell-dollars/index.js
index 50a7a12..4dcc3ab 100644
--- a/packages/remark-lint-no-shell-dollars/index.js
+++ b/packages/remark-lint-no-shell-dollars/index.js
@@ -90,6 +90,7 @@
  * @typedef {import('mdast').Root} Root
  */
 
+import {collapseWhiteSpace} from 'collapse-white-space'
 import {lintRule} from 'unified-lint-rule'
 import {position} from 'unist-util-position'
 import {visit} from 'unist-util-visit'
@@ -140,23 +141,27 @@ const remarkLintNoShellDollars = lintRule(
 
       // Check known shell code.
       if (place && node.lang && flags.has(node.lang)) {
-        const lines = node.value.split('\n').filter(function (line) {
-          return line.trim().length > 0
-        })
+        const lines = node.value.split('\n')
         let index = -1
 
-        if (lines.length === 0) {
-          return
-        }
+        let hasLines = false
 
         while (++index < lines.length) {
-          const line = lines[index].trim()
+          const line = collapseWhiteSpace(lines[index], {style: 'html'})
+
+          if (!line) continue
+
+          hasLines = true
 
           if (!/^\$/.test(line)) {
             return
           }
         }
 
+        if (!hasLines) {
+          return
+        }
+
         file.message('Do not use dollar signs before shell commands', place)
       }
     })
diff --git a/packages/remark-lint-no-shell-dollars/package.json b/packages/remark-lint-no-shell-dollars/package.json
index cc3557f..616b17b 100644
--- a/packages/remark-lint-no-shell-dollars/package.json
+++ b/packages/remark-lint-no-shell-dollars/package.json
@@ -32,6 +32,7 @@
   ],
   "dependencies": {
     "@types/mdast": "^4.0.0",
+    "collapse-white-space": "^2.0.0",
     "unified-lint-rule": "^2.0.0",
     "unist-util-position": "^5.0.0",
     "unist-util-visit": "^5.0.0"
diff --git a/packages/remark-lint-no-table-indentation/index.js b/packages/remark-lint-no-table-indentation/index.js
index 24e0fd5..603cab0 100644
--- a/packages/remark-lint-no-table-indentation/index.js
+++ b/packages/remark-lint-no-table-indentation/index.js
@@ -138,8 +138,8 @@ const remarkLintNoTableIndentation = lintRule(
         const head = parent.children[0]
         column = pointStart(head)?.column
 
-        // Skip past the first line if we’re the first child of a list item.
-        /* c8 ignore next 3 */
+        /* c8 ignore next 4 -- skip past the first line if we’re the first
+         * child of a list item. */
         if (typeof line === 'number' && head === node) {
           line++
         }
diff --git a/packages/remark-lint-no-table-indentation/readme.md b/packages/remark-lint-no-table-indentation/readme.md
index f4fe7fe..4d38992 100644
--- a/packages/remark-lint-no-table-indentation/readme.md
+++ b/packages/remark-lint-no-table-indentation/readme.md
@@ -152,7 +152,8 @@ So it’s recommended to not indent tables and to turn this rule on.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 Paragraph.
@@ -170,7 +171,8 @@ No messages.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 Paragraph.
@@ -192,7 +194,8 @@ Paragraph.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 >␠␠| A |
@@ -209,7 +212,8 @@ Paragraph.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 -␠␠␠paragraph
diff --git a/packages/remark-lint-no-undefined-references/index.js b/packages/remark-lint-no-undefined-references/index.js
index d49ab6d..2c8e54d 100644
--- a/packages/remark-lint-no-undefined-references/index.js
+++ b/packages/remark-lint-no-undefined-references/index.js
@@ -213,9 +213,9 @@ const remarkLintNoUndefinedReferences = lintRule(
 
     visit(tree, function (node) {
       const place = position(node)
-      // CM specifiers that references only form when defined.
-      // Still, they could be added by plugins, so let’s keep it.
-      /* c8 ignore next 10 */
+      /* c8 ignore next 12 -- CM specifies that references only form when
+       * defined.
+       * Still, they could be added by plugins, so let’s keep it. */
       if (
         (node.type === 'imageReference' ||
           node.type === 'linkReference' ||
diff --git a/packages/remark-lint-no-unneeded-full-reference-image/index.js b/packages/remark-lint-no-unneeded-full-reference-image/index.js
index 2801ee4..a12815b 100644
--- a/packages/remark-lint-no-unneeded-full-reference-image/index.js
+++ b/packages/remark-lint-no-unneeded-full-reference-image/index.js
@@ -92,7 +92,7 @@ const remarkLintNoUnneededFullReferenceImage = lintRule(
       if (
         !place ||
         node.referenceType !== 'full' ||
-        /* c8 ignore next */
+        /* c8 ignore next -- generated AST can omit `alt`. */
         normalizeIdentifier(node.alt || '') !== node.identifier.toUpperCase()
       ) {
         return
diff --git a/packages/remark-lint-no-unused-definitions/index.js b/packages/remark-lint-no-unused-definitions/index.js
index 83c13ef..3884e47 100644
--- a/packages/remark-lint-no-unused-definitions/index.js
+++ b/packages/remark-lint-no-unused-definitions/index.js
@@ -62,11 +62,12 @@
  * @example
  *   {"name": "footnote.md", "gfm": true, "label": "output"}
  *
- *   4:1-4:13: Found unused definition
+ *   4:1-4:13: Found unused footnote definition
  */
 
 /**
- * @typedef {import('mdast').DefinitionContent} DefinitionContent
+ * @typedef {import('mdast').Definition} Definition
+ * @typedef {import('mdast').FootnoteDefinition} FootnoteDefinition
  * @typedef {import('mdast').Root} Root
  */
 
@@ -86,13 +87,19 @@ const remarkLintNoUnusedDefinitions = lintRule(
    *   Nothing.
    */
   function (tree, file) {
-    /** @type {Map<string, {node: DefinitionContent | undefined, used: boolean}>} */
-    const map = new Map()
+    /** @type {Map<string, {node: Definition | FootnoteDefinition | undefined, used: boolean}>} */
+    const footnoteDefinitions = new Map()
+    /** @type {Map<string, {node: Definition | FootnoteDefinition | undefined, used: boolean}>} */
+    const definitions = new Map()
 
-    // To do: separate maps for footnotes/definitions.
     visit(tree, function (node) {
       if ('identifier' in node) {
         const id = node.identifier.toLowerCase()
+        const map =
+          node.type === 'footnoteDefinition' ||
+          node.type === 'footnoteReference'
+            ? footnoteDefinitions
+            : definitions
         let entry = map.get(id)
 
         if (!entry) {
@@ -112,7 +119,15 @@ const remarkLintNoUnusedDefinitions = lintRule(
       }
     })
 
-    for (const entry of map.values()) {
+    for (const entry of footnoteDefinitions.values()) {
+      const place = position(entry.node)
+
+      if (place && !entry.used) {
+        file.message('Found unused footnote definition', place)
+      }
+    }
+
+    for (const entry of definitions.values()) {
       const place = position(entry.node)
 
       if (place && !entry.used) {
diff --git a/packages/remark-lint-no-unused-definitions/readme.md b/packages/remark-lint-no-unused-definitions/readme.md
index fe3d88c..ba56b3a 100644
--- a/packages/remark-lint-no-unused-definitions/readme.md
+++ b/packages/remark-lint-no-unused-definitions/readme.md
@@ -170,7 +170,8 @@ No messages.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 a[^x].
@@ -182,7 +183,7 @@ a[^x].
 ###### Out
 
 ```text
-4:1-4:13: Found unused definition
+4:1-4:13: Found unused footnote definition
 ```
 
 ## Compatibility
diff --git a/packages/remark-lint-strikethrough-marker/readme.md b/packages/remark-lint-strikethrough-marker/readme.md
index a0451bd..f07af21 100644
--- a/packages/remark-lint-strikethrough-marker/readme.md
+++ b/packages/remark-lint-strikethrough-marker/readme.md
@@ -177,7 +177,8 @@ When configured with `'~'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 ~foo~
@@ -193,7 +194,8 @@ When configured with `'~'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 ~~foo~~
@@ -211,7 +213,8 @@ When configured with `'~~'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 ~~foo~~
@@ -227,7 +230,8 @@ When configured with `'~~'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 ~foo~
@@ -243,7 +247,8 @@ When configured with `'~~'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 ~~foo~~
diff --git a/packages/remark-lint-table-cell-padding/index.js b/packages/remark-lint-table-cell-padding/index.js
index 4d3e74f..8afbeef 100644
--- a/packages/remark-lint-table-cell-padding/index.js
+++ b/packages/remark-lint-table-cell-padding/index.js
@@ -271,7 +271,7 @@ const remarkLintTableCellPadding = lintRule(
 
     visit(tree, 'table', function (node) {
       const rows = node.children
-      /* c8 ignore next -- to do: fix types to always have `align` defined. */
+      /* c8 ignore next -- generated AST can omit `align`. */
       const align = node.align || []
       /** @type {Array<number>} */
       const sizes = []
@@ -414,7 +414,6 @@ export default remarkLintTableCellPadding
 function size(node) {
   const head = pointStart(node.children[0])?.offset
   const tail = pointEnd(node.children[node.children.length - 1])?.offset
-  // Only called when we’re sure offsets exist.
-  /* c8 ignore next */
+  /* c8 ignore next -- Only called when we’re sure offsets exist. */
   return typeof head === 'number' && typeof tail === 'number' ? tail - head : 0
 }
diff --git a/packages/remark-lint-table-cell-padding/readme.md b/packages/remark-lint-table-cell-padding/readme.md
index ba4e21e..354d219 100644
--- a/packages/remark-lint-table-cell-padding/readme.md
+++ b/packages/remark-lint-table-cell-padding/readme.md
@@ -186,7 +186,8 @@ When configured with `'padded'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 | A     | B     |
@@ -204,7 +205,8 @@ When configured with `'padded'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 | A    |    B |
@@ -242,7 +244,8 @@ When configured with `'compact'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 |A    |B    |
@@ -260,7 +263,8 @@ When configured with `'compact'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 |   A    | B    |
@@ -284,7 +288,8 @@ When configured with `'compact'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 The default is `'consistent'`.
@@ -308,7 +313,8 @@ When configured with `'consistent'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 | A     | B     |
@@ -332,7 +338,8 @@ When configured with `'consistent'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 |A    |B    |
@@ -354,7 +361,8 @@ When configured with `'consistent'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 |A    |B    |
@@ -388,7 +396,8 @@ When configured with `'padded'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 <!-- Empty cells are OK, but those surrounding them may not be. -->
@@ -412,7 +421,8 @@ When configured with `'padded'`.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 <!-- Missing cells are fine as well. -->
diff --git a/packages/remark-lint-table-pipe-alignment/readme.md b/packages/remark-lint-table-pipe-alignment/readme.md
index caf9e7e..31c8dc3 100644
--- a/packages/remark-lint-table-pipe-alignment/readme.md
+++ b/packages/remark-lint-table-pipe-alignment/readme.md
@@ -160,7 +160,8 @@ in which case this rule must be turned off.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 | A     | B     |
@@ -176,7 +177,8 @@ No messages.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 | A | B |
@@ -195,7 +197,8 @@ No messages.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 | | B     |   |
@@ -211,7 +214,8 @@ No messages.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 |   |     |         |
diff --git a/packages/remark-lint-table-pipes/readme.md b/packages/remark-lint-table-pipes/readme.md
index c45048f..2bf9e48 100644
--- a/packages/remark-lint-table-pipes/readme.md
+++ b/packages/remark-lint-table-pipes/readme.md
@@ -153,7 +153,8 @@ delimiters.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 | A     | B     |
@@ -169,7 +170,8 @@ No messages.
 
 ###### In
 
-> 👉 **Note**: this example uses GFM ([`remark-gfm`][github-remark-gfm]).
+> 👉 **Note**: this example uses
+> GFM ([`remark-gfm`][github-remark-gfm]).
 
 ```markdown
 A     | B
diff --git a/packages/unified-lint-rule/lib/index.js b/packages/unified-lint-rule/lib/index.js
index 5f3c6d3..3a74422 100644
--- a/packages/unified-lint-rule/lib/index.js
+++ b/packages/unified-lint-rule/lib/index.js
@@ -56,8 +56,7 @@ export function lintRule(meta, rule) {
   const id = typeof meta === 'string' ? meta : meta.origin
   const url = typeof meta === 'string' ? undefined : meta.url
   const parts = id.split(':')
-  // Possibly useful if externalised later.
-  /* c8 ignore next */
+  /* c8 ignore next -- Possibly useful if externalised later. */
   const source = parts[1] ? parts[0] : undefined
   const ruleId = parts[1]
 
@@ -94,9 +93,9 @@ export function lintRule(meta, rule) {
       wrap(rule, function (error) {
         const messages = file.messages
 
-        // Add the error, if not already properly added.
-        // Only happens for incorrect plugins.
-        /* c8 ignore next 6 */
+        /* c8 ignore next 8 -- add the error,
+         * if not already properly added.
+         * Only happens for incorrect plugins. */
         // @ts-expect-error: errors could be `messages`.
         if (error && !messages.includes(error)) {
           try {
diff --git a/script/info.js b/script/info.js
index 6167eb4..c16a85c 100644
--- a/script/info.js
+++ b/script/info.js
@@ -12,6 +12,8 @@
  *   Whether to use GFM.
  * @property {string} input
  *   Input.
+ * @property {boolean} mdx
+ *   Whether to use MDX.
  * @property {string} name
  *   Name.
  * @property {Array<string>} output
@@ -27,6 +29,8 @@
  *   Whether to use GFM (optional).
  * @property {'input' | 'output'} [label]
  *   Label (optional).
+ * @property {boolean} [mdx]
+ *   Whether to use MDX (optional).
  * @property {boolean} [positionless]
  *   Whether this check also applies without positions (optional).
  * @property {string} name
@@ -168,7 +172,14 @@ async function addPlugin(name) {
       throw new Error('Could not parse example in `' + ruleId + '`', {cause})
     }
 
-    const exampleValue = strip(lines.join('\n').replace(/^\r?\n/g, ''))
+    const exampleValue = strip(
+      lines
+        .join('\n')
+        // Remove head.
+        .replace(/^\r?\n/g, '')
+        // Remove magic handling of `nul` control picture.
+        .replace(/␀/g, '')
+    )
     const configuration = JSON.stringify({config: info.config || true})
     const name = info.name
 
@@ -179,6 +190,7 @@ async function addPlugin(name) {
         positionless: info.positionless || false,
         gfm: info.gfm || false,
         input: exampleValue,
+        mdx: info.mdx || false,
         output: []
       })
 
@@ -198,6 +210,7 @@ async function addPlugin(name) {
         positionless: info.positionless || false,
         gfm: info.gfm || false,
         input: '',
+        mdx: info.mdx || false,
         output: []
       }
       result.checks.push(found)
diff --git a/script/pipeline-package.js b/script/pipeline-package.js
index 27f32f2..f347e52 100644
--- a/script/pipeline-package.js
+++ b/script/pipeline-package.js
@@ -1255,6 +1255,10 @@ function generateReadmeExample(state) {
       'github-remark-gfm',
       'https://github.com/remarkjs/remark-gfm'
     )
+    state.urls.set(
+      'github-remark-mdx',
+      'https://mdxjs.com/packages/remark-mdx/'
+    )
 
     if (!empty) {
       children.push({
@@ -1263,8 +1267,40 @@ function generateReadmeExample(state) {
         children: [{type: 'text', value: 'In'}]
       })
 
-      // To do: other plugins.
+      /** @type {Array<PhrasingContent>} */
+      const phrasing = []
+
       if (check.gfm) {
+        phrasing.push(
+          {type: 'text', value: 'GFM ('},
+          {
+            type: 'linkReference',
+            identifier: 'github-remark-gfm',
+            referenceType: 'full',
+            children: [{type: 'inlineCode', value: 'remark-gfm'}]
+          },
+          {type: 'text', value: ')'}
+        )
+      }
+
+      if (check.mdx) {
+        if (phrasing.length > 0) {
+          phrasing.push({type: 'text', value: ',\n'})
+        }
+
+        phrasing.push(
+          {type: 'text', value: 'MDX ('},
+          {
+            type: 'linkReference',
+            identifier: 'github-remark-mdx',
+            referenceType: 'full',
+            children: [{type: 'inlineCode', value: 'remark-mdx'}]
+          },
+          {type: 'text', value: ')'}
+        )
+      }
+
+      if (phrasing.length > 0) {
         children.push({
           type: 'blockquote',
           children: [
@@ -1276,14 +1312,9 @@ function generateReadmeExample(state) {
                   type: 'strong',
                   children: [{type: 'text', value: 'Note'}]
                 },
-                {type: 'text', value: ': this example uses GFM ('},
-                {
-                  type: 'linkReference',
-                  identifier: 'github-remark-gfm',
-                  referenceType: 'full',
-                  children: [{type: 'inlineCode', value: 'remark-gfm'}]
-                },
-                {type: 'text', value: ').'}
+                {type: 'text', value: ': this example uses\n'},
+                ...phrasing,
+                {type: 'text', value: '.'}
               ]
             }
           ]
@@ -1292,7 +1323,7 @@ function generateReadmeExample(state) {
 
       children.push({
         type: 'code',
-        lang: 'markdown',
+        lang: check.mdx ? 'mdx' : 'markdown',
         value: check.input
       })
     }
diff --git a/test.js b/test.js
index 1ac29a7..6c8c40e 100644
--- a/test.js
+++ b/test.js
@@ -16,6 +16,7 @@ import remarkLintFinalNewline from 'remark-lint-final-newline'
 import remarkLintNoHeadingPunctuation from 'remark-lint-no-heading-punctuation'
 import remarkLintNoMultipleToplevelHeadings from 'remark-lint-no-multiple-toplevel-headings'
 import remarkLintNoUndefinedReferences from 'remark-lint-no-undefined-references'
+import remarkMdx from 'remark-mdx'
 import {lintRule} from 'unified-lint-rule'
 import {removePosition} from 'unist-util-remove-position'
 import {VFile} from 'vfile'
@@ -81,9 +82,12 @@ test('remark-lint', async function (t) {
 
     assert.deepEqual(file.messages.map(jsonClone), [
       {
+        column: 2,
         fatal: true,
+        line: 1,
         message: 'Missing newline character at end of file',
-        name: '1:1',
+        name: '1:2',
+        place: {column: 2, line: 1, offset: 1},
         reason: 'Missing newline character at end of file',
         ruleId: 'final-newline',
         source: 'remark-lint',
@@ -96,7 +100,7 @@ test('remark-lint', async function (t) {
     const file = await remark().use(remarkLintFinalNewline, true).process('.')
 
     assert.deepEqual(file.messages.map(String), [
-      '1:1: Missing newline character at end of file'
+      '1:2: Missing newline character at end of file'
     ])
   })
 
@@ -114,7 +118,7 @@ test('remark-lint', async function (t) {
         .process('.')
 
       assert.deepEqual(file.messages.map(String), [
-        '1:1: Missing newline character at end of file'
+        '1:2: Missing newline character at end of file'
       ])
     }
   )
@@ -139,9 +143,12 @@ test('remark-lint', async function (t) {
 
       assert.deepEqual(file.messages.map(jsonClone), [
         {
+          column: 2,
           fatal: true,
+          line: 1,
           message: 'Missing newline character at end of file',
-          name: '1:1',
+          name: '1:2',
+          place: {column: 2, line: 1, offset: 1},
           reason: 'Missing newline character at end of file',
           ruleId: 'final-newline',
           source: 'remark-lint',
@@ -160,9 +167,12 @@ test('remark-lint', async function (t) {
 
       assert.deepEqual(file.messages.map(jsonClone), [
         {
+          column: 2,
           fatal: false,
+          line: 1,
           message: 'Missing newline character at end of file',
-          name: '1:1',
+          name: '1:2',
+          place: {column: 2, line: 1, offset: 1},
           reason: 'Missing newline character at end of file',
           ruleId: 'final-newline',
           source: 'remark-lint',
@@ -181,9 +191,12 @@ test('remark-lint', async function (t) {
 
       assert.deepEqual(file.messages.map(jsonClone), [
         {
+          column: 2,
           fatal: false,
+          line: 1,
           message: 'Missing newline character at end of file',
-          name: '1:1',
+          name: '1:2',
+          place: {column: 2, line: 1, offset: 1},
           reason: 'Missing newline character at end of file',
           ruleId: 'final-newline',
           source: 'remark-lint',
@@ -302,9 +315,17 @@ async function assertCheck(plugin, info, check) {
   /** @type {{config: unknown}} */
   const {config} = JSON.parse(check.configuration)
   /** @type {PluggableList} */
-  const extras = check.gfm ? [remarkGfm] : []
+  const extras = []
   const value = controlPictures(check.input)
 
+  if (check.gfm) {
+    extras.push(remarkGfm)
+  }
+
+  if (check.mdx) {
+    extras.push(remarkMdx)
+  }
+
   const file = await remark()
     .use(plugin, config)
     .use(extras)