diff --git a/.gitignore b/.gitignore
index 735f4af..53a29e3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
-.DS_Store
-*.log
 coverage/
 node_modules/
+.DS_Store
+*.d.ts
+*.log
 yarn.lock
diff --git a/index.d.ts b/index.d.ts
deleted file mode 100644
index 953eba0..0000000
--- a/index.d.ts
+++ /dev/null
@@ -1,116 +0,0 @@
-// TypeScript Version: 3.4
-
-import {Node} from 'unist'
-import {Transformer} from 'unified'
-import {Test} from 'unist-util-is'
-
-declare namespace messageControl {
-  /**
-   * A comment marker.
-   */
-  interface Marker<N extends Node> {
-    /**
-     * Name of marker
-     */
-    name: string
-
-    /**
-     * Value after name
-     */
-    attributes: string
-
-    /**
-     * Parsed attributes
-     */
-    parameters: Record<string, unknown>
-
-    /**
-     * Reference to given node
-     */
-    node: N
-  }
-
-  /**
-   * Parse a possible comment marker node to a Marker
-   */
-  type MarkerParser<N extends Node> = (node: N) => Marker<N> | null
-
-  interface MessageControlOptionsWithReset<T extends Node>
-    extends BaseMessageControlOptions<T> {
-    /**
-     * Whether to treat all messages as turned off initially
-     */
-    reset: true
-
-    /**
-     * List of `ruleId`s to initially turn on.
-     */
-    enable?: string[]
-  }
-
-  interface MessageControlOptionsWithoutReset<T extends Node>
-    extends BaseMessageControlOptions<T> {
-    /**
-     * Whether to treat all messages as turned off initially
-     */
-    reset?: false
-
-    /**
-     * List of `ruleId`s to turn off
-     */
-    disable?: string[]
-  }
-
-  interface BaseMessageControlOptions<T extends Node> {
-    /**
-     * Name of markers that can control the message sources.
-     *
-     * For example. `{name: 'alpha'}` controls `alpha` markers:
-     *
-     * `<!--alpha ignore-->`
-     */
-    name: string
-
-    /**
-     * Test for possible markers
-     */
-    test: Test<T>
-
-    /**
-     * Parse a possible marker to a comment marker object (Marker)
-     * if possible the marker isn't a marker, should return `null`.
-     */
-    marker: MarkerParser<T>
-
-    /**
-     * List of allowed `ruleId`s. When given a warning is shown
-     * when someone tries to control an unknown rule.
-     *
-     * For example, `{name: 'alpha', known: ['bravo']}` results
-     * in a warning if `charlie is configured:
-     *
-     * `<!--alpha ignore charlie-->`
-     */
-    known?: string[]
-
-    /**
-     * Sources that can be controlled with `name` markers.
-     *
-     * @defaultValue `MessageControlOptions.name`
-     */
-    sources?: string | string[]
-  }
-
-  type MessageControlOptions<T extends Node> =
-    | MessageControlOptionsWithoutReset<T>
-    | MessageControlOptionsWithReset<T>
-}
-
-/**
- * Enable, disable, and ignore messages with unified.
- */
-declare function messageControl<T extends Node>(
-  options?: messageControl.MessageControlOptions<T>
-): Transformer
-
-export = messageControl
diff --git a/index.js b/index.js
index 5bcbab2..0719e92 100644
--- a/index.js
+++ b/index.js
@@ -1,60 +1,149 @@
+/**
+ * @typedef {import('unist').Node} Node
+ * @typedef {import('unist').Parent} Parent
+ * @typedef {import('unist').Point} Point
+ * @typedef {import('unist-util-is').Test} Test
+ * @typedef {import('vfile').VFile} VFile
+ * @typedef {import('vfile-message').VFileMessage} VFileMessage
+ *
+ * @typedef {OptionsWithoutReset|OptionsWithReset} Options
+ * @typedef {OptionsBaseFields & OptionsWithoutResetFields} OptionsWithoutReset
+ * @typedef {OptionsBaseFields & OptionsWithResetFields} OptionsWithReset
+ *
+ * @typedef OptionsWithoutResetFields
+ * @property {false} [reset]
+ *   Whether to treat all messages as turned off initially.
+ * @property {string[]} [disable]
+ *   List of `ruleId`s to turn off.
+ *
+ * @typedef OptionsWithResetFields
+ * @property {true} reset
+ *   Whether to treat all messages as turned off initially.
+ * @property {string[]} [enable]
+ *   List of `ruleId`s to initially turn on.
+ *
+ * @typedef OptionsBaseFields
+ * @property {string} name
+ *   Name of markers that can control the message sources.
+ *
+ *   For example, `{name: 'alpha'}` controls `alpha` markers:
+ *
+ *   ```html
+ *   <!--alpha ignore-->
+ *   ```
+ * @property {MarkerParser} marker
+ *   Parse a possible marker to a comment marker object (Marker).
+ *   If the marker isn't a marker, should return `null`.
+ * @property {Test} [test]
+ *   Test for possible markers
+ * @property {string[]} [known]
+ *   List of allowed `ruleId`s. When given a warning is shown
+ *   when someone tries to control an unknown rule.
+ *
+ *   For example, `{name: 'alpha', known: ['bravo']}` results in a warning if
+ *   `charlie` is configured:
+ *
+ *   ```html
+ *   <!--alpha ignore charlie-->
+ *   ```
+ * @property {string|string[]} [source]
+ *   Sources that can be controlled with `name` markers.
+ *   Defaults to `name`.
+ *
+ * @callback MarkerParser
+ *   Parse a possible comment marker node to a Marker.
+ * @param {Node} node
+ *   Node to parse
+ *
+ * @typedef Marker
+ *   A comment marker.
+ * @property {string} name
+ *   Name of marker.
+ * @property {string} attributes
+ *   Value after name.
+ * @property {Record<string, string|number|boolean>} parameters
+ *   Parsed attributes.
+ * @property {Node} node
+ *   Reference to given node.
+ *
+ * @typedef Mark
+ * @property {Point|undefined} point
+ * @property {boolean} state
+ */
+
 import {location} from 'vfile-location'
 import {visit} from 'unist-util-visit'
 
 const own = {}.hasOwnProperty
 
+/**
+ * @param {Options} options
+ */
 export function messageControl(options) {
-  const settings = options || {}
-  const enable = settings.enable || []
-  const disable = settings.disable || []
-  let sources = settings.source
-  let reset = settings.reset
-
-  if (!settings.name) {
-    throw new Error('Expected `name` in `options`, got `' + settings.name + '`')
+  if (!options || typeof options !== 'object' || !options.name) {
+    throw new Error(
+      'Expected `name` in `options`, got `' + (options || {}).name + '`'
+    )
   }
 
-  if (!settings.marker) {
+  if (!options.marker) {
     throw new Error(
-      'Expected `marker` in `options`, got `' + settings.marker + '`'
+      'Expected `marker` in `options`, got `' + options.marker + '`'
     )
   }
 
-  if (!sources) {
-    sources = [settings.name]
-  } else if (typeof sources === 'string') {
-    sources = [sources]
-  }
+  const enable = 'enable' in options && options.enable ? options.enable : []
+  const disable = 'disable' in options && options.disable ? options.disable : []
+  let reset = options.reset
+  const sources =
+    typeof options.source === 'string'
+      ? [options.source]
+      : options.source || [options.name]
 
   return transformer
 
+  /**
+   * @param {Node} tree
+   * @param {VFile} file
+   */
   function transformer(tree, file) {
     const toOffset = location(file).toOffset
     const initial = !reset
     const gaps = detectGaps(tree, file)
+    /** @type {Record<string, Mark[]>} */
     const scope = {}
+    /** @type {Mark[]} */
     const globals = []
 
-    visit(tree, settings.test, visitor)
+    visit(tree, options.test, visitor)
 
     file.messages = file.messages.filter((m) => filter(m))
 
+    /**
+     * @param {Node} node
+     * @param {number|null} position
+     * @param {Parent|null} parent
+     */
     function visitor(node, position, parent) {
-      const mark = settings.marker(node)
+      /** @type {Marker|null} */
+      const mark = options.marker(node)
 
-      if (!mark || mark.name !== settings.name) {
+      if (!mark || mark.name !== options.name) {
         return
       }
 
       const ruleIds = mark.attributes.split(/\s/g)
-      const verb = ruleIds.shift()
-      const pos = mark.node.position && mark.node.position.start
-      const tail =
-        parent.children[position + 1] &&
-        parent.children[position + 1].position &&
-        parent.children[position + 1].position.end
+      const point = mark.node.position && mark.node.position.start
+      const next =
+        (parent && position !== null && parent.children[position + 1]) ||
+        undefined
+      const tail = (next && next.position && next.position.end) || undefined
       let index = -1
 
+      /** @type {string} */
+      // @ts-expect-error: we’ll check for unknown values next.
+      const verb = ruleIds.shift()
+
       if (verb !== 'enable' && verb !== 'disable' && verb !== 'ignore') {
         file.fail(
           'Unknown keyword `' +
@@ -71,7 +160,7 @@ export function messageControl(options) {
           const ruleId = ruleIds[index]
 
           if (isKnown(ruleId, verb, mark.node)) {
-            toggle(pos, verb === 'enable', ruleId)
+            toggle(point, verb === 'enable', ruleId)
 
             if (verb === 'ignore') {
               toggle(tail, true, ruleId)
@@ -79,14 +168,18 @@ export function messageControl(options) {
           }
         }
       } else if (verb === 'ignore') {
-        toggle(pos, false)
+        toggle(point, false)
         toggle(tail, true)
       } else {
-        toggle(pos, verb === 'enable')
+        toggle(point, verb === 'enable')
         reset = verb !== 'enable'
       }
     }
 
+    /**
+     * @param {VFileMessage} message
+     * @returns {boolean}
+     */
     function filter(message) {
       let gapIndex = gaps.length
 
@@ -106,37 +199,51 @@ export function messageControl(options) {
       }
 
       // Check whether the warning is inside a gap.
-      const pos = toOffset(message)
+      // @ts-expect-error: we just normalized `null` to `number`s.
+      const offset = toOffset(message)
 
       while (gapIndex--) {
-        if (gaps[gapIndex].start <= pos && gaps[gapIndex].end > pos) {
+        if (gaps[gapIndex][0] <= offset && gaps[gapIndex][1] > offset) {
           return false
         }
       }
 
       // Check whether allowed by specific and global states.
       return (
-        check(message, scope[message.ruleId], message.ruleId) &&
+        (!message.ruleId ||
+          check(message, scope[message.ruleId], message.ruleId)) &&
         check(message, globals)
       )
     }
 
-    // Helper to check (and possibly warn) if a `ruleId` is unknown.
-    function isKnown(ruleId, verb, pos) {
-      const result = settings.known ? settings.known.includes(ruleId) : true
+    /**
+     * Helper to check (and possibly warn) if a `ruleId` is unknown.
+     *
+     * @param {string} ruleId
+     * @param {string} verb
+     * @param {Node} node
+     * @returns {boolean}
+     */
+    function isKnown(ruleId, verb, node) {
+      const result = options.known ? options.known.includes(ruleId) : true
 
       if (!result) {
         file.message(
           'Unknown rule: cannot ' + verb + " `'" + ruleId + "'`",
-          pos
+          node
         )
       }
 
       return result
     }
 
-    // Get the latest state of a rule.
-    // When without `ruleId`, gets global state.
+    /**
+     * Get the latest state of a rule.
+     * When without `ruleId`, gets global state.
+     *
+     * @param {string|undefined} ruleId
+     * @returns {boolean}
+     */
     function getState(ruleId) {
       const ranges = ruleId ? scope[ruleId] : globals
 
@@ -151,53 +258,73 @@ export function messageControl(options) {
       return reset ? enable.includes(ruleId) : !disable.includes(ruleId)
     }
 
-    // Handle a rule.
-    function toggle(pos, state, ruleId) {
+    /**
+     * Handle a rule.
+     *
+     * @param {Point|undefined} point
+     * @param {boolean} state
+     * @param {string|undefined} [ruleId]
+     * @returns {void}
+     */
+    function toggle(point, state, ruleId) {
       let markers = ruleId ? scope[ruleId] : globals
 
       if (!markers) {
         markers = []
-        scope[ruleId] = markers
+        scope[String(ruleId)] = markers
       }
 
       const previousState = getState(ruleId)
 
       if (state !== previousState) {
-        markers.push({state, position: pos})
+        markers.push({state, point})
       }
 
       // Toggle all known rules.
       if (!ruleId) {
         for (ruleId in scope) {
           if (own.call(scope, ruleId)) {
-            toggle(pos, state, ruleId)
+            toggle(point, state, ruleId)
           }
         }
       }
     }
 
-    // Check all `ranges` for `message`.
+    /**
+     * Check all `ranges` for `message`.
+     *
+     * @param {VFileMessage} message
+     * @param {Mark[]|undefined} ranges
+     * @param {string|undefined} [ruleId]
+     * @returns {boolean}
+     */
     function check(message, ranges, ruleId) {
-      // Check the state at the message’s position.
-      let index = ranges ? ranges.length : 0
-
-      while (index--) {
-        if (
-          ranges[index].position &&
-          ranges[index].position.line &&
-          ranges[index].position.column &&
-          (ranges[index].position.line < message.line ||
-            (ranges[index].position.line === message.line &&
-              ranges[index].position.column <= message.column))
-        ) {
-          return ranges[index].state === true
+      if (ranges && ranges.length > 0) {
+        // Check the state at the message’s position.
+        let index = ranges.length
+
+        while (index--) {
+          const range = ranges[index]
+
+          if (
+            message.line &&
+            message.column &&
+            range.point &&
+            range.point.line &&
+            range.point.column &&
+            (range.point.line < message.line ||
+              (range.point.line === message.line &&
+                range.point.column <= message.column))
+          ) {
+            return range.state === true
+          }
         }
       }
 
       // The first marker ocurred after the first message, so we check the
       // initial state.
       if (!ruleId) {
-        return initial || reset
+        return Boolean(initial || reset)
       }
 
       return reset ? enable.includes(ruleId) : !disable.includes(ruleId)
@@ -205,12 +332,21 @@ export function messageControl(options) {
   }
 }
 
-// Detect gaps in `tree`.
+/**
+ * Detect gaps in `tree`.
+ *
+ * @param {Node} tree
+ * @param {VFile} file
+ */
 function detectGaps(tree, file) {
+  /** @type {Node[]} */
+  // @ts-expect-error: fine.
   const children = tree.children || []
   const lastNode = children[children.length - 1]
+  /** @type {[number, number][]} */
   const gaps = []
   let offset = 0
+  /** @type {boolean|undefined} */
   let gap
 
   // Find all gaps.
@@ -230,28 +366,40 @@ function detectGaps(tree, file) {
     update()
 
     update(
-      tree && tree.position && tree.position.end && tree.position.end.offset - 1
+      tree &&
+        tree.position &&
+        tree.position.end &&
+        tree.position.end.offset &&
+        tree.position.end.offset - 1
     )
   }
 
   return gaps
 
+  /**
+   * @param {Node} node
+   */
   function one(node) {
     update(node.position && node.position.start && node.position.start.offset)
 
-    if (!node.children) {
+    if (!('children' in node)) {
       update(node.position && node.position.end && node.position.end.offset)
     }
   }
 
-  // Detect a new position.
+  /**
+   * Detect a new position.
+   *
+   * @param {number|undefined} [latest]
+   * @returns {void}
+   */
   function update(latest) {
     if (latest === null || latest === undefined) {
       gap = true
     } else if (offset < latest) {
       if (gap) {
-        gaps.push({start: offset, end: latest})
-        gap = null
+        gaps.push([offset, latest])
+        gap = undefined
       }
 
       offset = latest
diff --git a/package.json b/package.json
index 33730fb..d93e29f 100644
--- a/package.json
+++ b/package.json
@@ -32,13 +32,15 @@
     "index.js"
   ],
   "dependencies": {
+    "@types/unist": "^2.0.0",
+    "unist-util-is": "^5.0.0",
     "unist-util-visit": "^3.0.0",
-    "vfile-location": "^4.0.0"
+    "vfile": "^5.0.0",
+    "vfile-location": "^4.0.0",
+    "vfile-message": "^3.0.0"
   },
   "devDependencies": {
-    "@types/hast": "^2.0.0",
-    "@types/mdast": "^3.0.0",
-    "@types/unist": "^2.0.0",
+    "@types/tape": "^4.0.0",
     "c8": "^7.0.0",
     "mdast-comment-marker": "^2.0.0",
     "prettier": "^2.0.0",
@@ -46,17 +48,19 @@
     "remark-cli": "^9.0.0",
     "remark-preset-wooorm": "^8.0.0",
     "remark-toc": "^7.0.0",
+    "rimraf": "^3.0.0",
     "tape": "^5.0.0",
+    "type-coverage": "^2.0.0",
+    "typescript": "^4.0.0",
     "unified": "^10.0.0-beta.1",
-    "unist-util-is": "^5.0.0",
     "xo": "^0.39.0"
   },
   "scripts": {
+    "build": "rimraf \"*.d.ts\" && tsc && type-coverage",
     "format": "remark . -qfo && prettier . -w --loglevel warn && xo --fix",
     "test-api": "node --conditions development test.js",
     "test-coverage": "c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 --reporter lcov node --conditions development test.js",
-    "xxx-test-types": "dtslint",
-    "test": "npm run format && npm run test-coverage"
+    "test": "npm run build && npm run format && npm run test-coverage"
   },
   "prettier": {
     "tabWidth": 2,
@@ -67,14 +71,17 @@
     "trailingComma": "none"
   },
   "xo": {
-    "prettier": true,
-    "ignores": [
-      "*.ts"
-    ]
+    "prettier": true
   },
   "remarkConfig": {
     "plugins": [
       "preset-wooorm"
     ]
+  },
+  "typeCoverage": {
+    "atLeast": 100,
+    "detail": true,
+    "strict": true,
+    "ignoreCatch": true
   }
 }
diff --git a/test.js b/test.js
index d7bcb13..0f37025 100644
--- a/test.js
+++ b/test.js
@@ -1,12 +1,21 @@
+/**
+ * @typedef {import('unist').Node} Node
+ */
+
 import test from 'tape'
-import remark from 'remark'
+import {unified} from 'unified'
+import remarkParse from 'remark-parse'
+import remarkStringify from 'remark-stringify'
 import remarkToc from 'remark-toc'
 import {commentMarker} from 'mdast-comment-marker'
 import {messageControl} from './index.js'
 
+const remark = unified().use(remarkParse).use(remarkStringify).freeze()
+
 test('messageControl()', (t) => {
   t.throws(
     () => {
+      // @ts-expect-error: runtime.
       remark().use(messageControl).freeze()
     },
     /Expected `name` in `options`, got `undefined`/,
@@ -15,6 +24,7 @@ test('messageControl()', (t) => {
 
   t.throws(
     () => {
+      // @ts-expect-error: runtime.
       remark().use(messageControl, {name: 'foo'}).freeze()
     },
     /Expected `marker` in `options`, got `undefined`/,
@@ -36,6 +46,7 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1], 'foo:bar')
         transformer(tree, file)
       }
@@ -44,7 +55,7 @@ test('messageControl()', (t) => {
       '<!--foo disable bar-->\n\nThis is a paragraph.',
       (error, file) => {
         t.deepEqual(
-          [error].concat(file.messages),
+          [error, ...file.messages],
           [null],
           'should “disable” a message'
         )
@@ -60,6 +71,7 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1], 'foo:bar')
 
         transformer(tree, file)
@@ -67,7 +79,7 @@ test('messageControl()', (t) => {
     })
     .process('<!--foo disable-->\n\nThis is a paragraph.', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages),
+        [error, ...file.messages],
         [null],
         'should “disable” all message without `ruleId`s'
       )
@@ -83,7 +95,9 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[0], 'foo:bar')
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[2], 'foo:bar')
 
         transformer(tree, file)
@@ -99,7 +113,7 @@ test('messageControl()', (t) => {
       ].join('\n'),
       (error, file) => {
         t.deepEqual(
-          [error].concat(file.messages.map((m) => String(m))),
+          [error, ...file.messages.map((m) => String(m))],
           [null, '5:1-5:21: Error'],
           'should support `reset`'
         )
@@ -116,6 +130,7 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1], 'foo:bar')
 
         transformer(tree, file)
@@ -123,7 +138,7 @@ test('messageControl()', (t) => {
     })
     .process('<!--foo enable bar-->\n\nThis is a paragraph.', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null, '3:1-3:21: Error'],
         'should enable with a marker, when `reset`'
       )
@@ -138,7 +153,9 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1], 'foo:bar')
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[3], 'foo:bar')
 
         transformer(tree, file)
@@ -156,7 +173,7 @@ test('messageControl()', (t) => {
       ].join('\n'),
       (error, file) => {
         t.deepEqual(
-          [error].concat(file.messages.map((m) => String(m))),
+          [error, ...file.messages.map((m) => String(m))],
           [null, '7:1-7:21: Error'],
           'should enable a message'
         )
@@ -172,7 +189,9 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1], 'foo:bar')
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[3], 'foo:bar')
 
         transformer(tree, file)
@@ -190,7 +209,7 @@ test('messageControl()', (t) => {
       ].join('\n'),
       (error, file) => {
         t.deepEqual(
-          [error].concat(file.messages.map((m) => String(m))),
+          [error, ...file.messages.map((m) => String(m))],
           [null, '7:1-7:21: Error'],
           'should enable all message without `ruleId`s'
         )
@@ -206,7 +225,9 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1], 'foo:bar')
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[2], 'foo:bar')
 
         transformer(tree, file)
@@ -222,7 +243,7 @@ test('messageControl()', (t) => {
       ].join('\n'),
       (error, file) => {
         t.deepEqual(
-          [error].concat(file.messages.map((m) => String(m))),
+          [error, ...file.messages.map((m) => String(m))],
           [null, '5:1-5:21: Error'],
           'should ignore a message'
         )
@@ -238,7 +259,9 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1], 'foo:bar')
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[2], 'foo:bar')
 
         transformer(tree, file)
@@ -254,7 +277,7 @@ test('messageControl()', (t) => {
       ].join('\n'),
       (error, file) => {
         t.deepEqual(
-          [error].concat(file.messages.map((m) => String(m))),
+          [error, ...file.messages.map((m) => String(m))],
           [null, '5:1-5:21: Error'],
           'should ignore all message without `ruleId`s'
         )
@@ -270,7 +293,9 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1], 'foo:bar')
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1], 'foo:baz')
 
         transformer(tree, file)
@@ -280,7 +305,7 @@ test('messageControl()', (t) => {
       '<!--foo ignore bar baz-->\n\nThis is a paragraph.',
       (error, file) => {
         t.deepEqual(
-          [error].concat(file.messages.map((m) => String(m))),
+          [error, ...file.messages.map((m) => String(m))],
           [null],
           'should ignore multiple rules'
         )
@@ -332,7 +357,7 @@ test('messageControl()', (t) => {
       ].join('\n'),
       (error, file) => {
         t.deepEqual(
-          [error].concat(file.messages.map((m) => String(m))),
+          [error, ...file.messages.map((m) => String(m))],
           [null, '7:1: Error'],
           'should ignore gaps'
         )
@@ -352,6 +377,7 @@ test('messageControl()', (t) => {
         file.message('Error', {line: 5, column: 1}, 'foo:bar')
 
         // Remove list.
+        // @ts-expect-error: fine.
         tree.children.pop()
 
         transformer(tree, file)
@@ -367,7 +393,7 @@ test('messageControl()', (t) => {
       ].join('\n'),
       (error, file) => {
         t.deepEqual(
-          [error].concat(file.messages.map((m) => String(m))),
+          [error, ...file.messages.map((m) => String(m))],
           [null],
           'should ignore final gaps'
         )
@@ -383,14 +409,14 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
-        file.message('Error', 'foo:bar')
+        file.message('Error', undefined, 'foo:bar')
 
         transformer(tree, file)
       }
     })
     .process('', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null, '1:1: Error'],
         'should support empty documents'
       )
@@ -405,6 +431,7 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.position.end, 'foo:bar')
 
         transformer(tree, file)
@@ -412,7 +439,7 @@ test('messageControl()', (t) => {
     })
     .process('# README\n', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null, '2:1: Error'],
         'should message at the end of the document'
       )
@@ -427,6 +454,7 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1].position.end, 'foo:bar')
 
         transformer(tree, file)
@@ -434,7 +462,7 @@ test('messageControl()', (t) => {
     })
     .process('# README\n\n*   List', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null, '3:9: Error'],
         'should message at the end of the document'
       )
@@ -449,7 +477,9 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1], 'foo:bar')
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[3], 'foo:bar')
 
         transformer(tree, file)
@@ -467,7 +497,7 @@ test('messageControl()', (t) => {
       ].join('\n'),
       (error, file) => {
         t.deepEqual(
-          [error].concat(file.messages.map((m) => String(m))),
+          [error, ...file.messages.map((m) => String(m))],
           [null],
           'should ignore double disables'
         )
@@ -483,14 +513,14 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
-        file.message('Error', 'foo:bar')
+        file.message('Error', undefined, 'foo:bar')
 
         transformer(tree, file)
       }
     })
     .process('Foo', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null, '1:1: Error'],
         'should not ignore messages without location information'
       )
@@ -506,7 +536,7 @@ test('messageControl()', (t) => {
     })
     .process('<!doctype html>\n\n<!--bar baz qux-->\n', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null],
         'should ignore non-markers'
       )
@@ -525,7 +555,7 @@ test('messageControl()', (t) => {
       '<!--foo ignore known-->\n\n<!--foo ignore unknown-->',
       (error, file) => {
         t.deepEqual(
-          [error].concat(file.messages.map((m) => String(m))),
+          [error, ...file.messages.map((m) => String(m))],
           [null, "3:1-3:26: Unknown rule: cannot ignore `'unknown'`"],
           'should support a list of `known` values, and warn on unknowns'
         )
@@ -542,6 +572,7 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1], 'baz:bar')
 
         transformer(tree, file)
@@ -549,7 +580,7 @@ test('messageControl()', (t) => {
     })
     .process('<!--foo ignore bar-->\n\nFoo', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null],
         'should ignore by `source`, when given as a string'
       )
@@ -565,7 +596,9 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[1], 'bravo:delta')
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[3], 'charlie:echo')
 
         transformer(tree, file)
@@ -583,7 +616,7 @@ test('messageControl()', (t) => {
       ].join('\n'),
       (error, file) => {
         t.deepEqual(
-          [error].concat(file.messages.map((m) => String(m))),
+          [error, ...file.messages.map((m) => String(m))],
           [null],
           'should ignore by `source`, when given as an array'
         )
@@ -600,6 +633,7 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[0], 'foo:bar')
 
         transformer(tree, file)
@@ -607,7 +641,7 @@ test('messageControl()', (t) => {
     })
     .process('This is a paragraph.', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null],
         'should support initial `disable`s'
       )
@@ -624,6 +658,7 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
+        // @ts-expect-error: fine.
         file.message('Error', tree.children[0], 'foo:bar')
 
         transformer(tree, file)
@@ -631,7 +666,7 @@ test('messageControl()', (t) => {
     })
     .process('This is a paragraph.', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null, '1:1-1:21: Error'],
         'should support initial `enable`s'
       )
@@ -653,7 +688,7 @@ test('messageControl()', (t) => {
     })
     .process('<!--foo disable bar-->\n', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null],
         'should disable messages at the start of a marker'
       )
@@ -676,7 +711,7 @@ test('messageControl()', (t) => {
     })
     .process('<!--foo enable-->\n', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null, '1:1: Error'],
         'should enable messages at the start of a marker'
       )
@@ -691,14 +726,14 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
-        file.message('Error', 'foo:bar')
+        file.message('Error', undefined, 'foo:bar')
 
         transformer(tree, file)
       }
     })
     .process('<!--foo disable bar-->\n', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null],
         'should disable messages without positional info (at the start of a document)'
       )
@@ -714,14 +749,14 @@ test('messageControl()', (t) => {
       })
 
       return function (tree, file) {
-        file.message('Error', 'foo:bar')
+        file.message('Error', undefined, 'foo:bar')
 
         transformer(tree, file)
       }
     })
     .process('<!--foo enable-->\n', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null, '1:1: Error'],
         'should enable messages without positional info (at the start of a document)'
       )
@@ -731,13 +766,14 @@ test('messageControl()', (t) => {
     .use(() => {
       return function (tree, file) {
         file.message('Error')
+        // @ts-expect-error: fine.
         delete tree.children
         messageControl({name: 'foo', marker: commentMarker})(tree, file)
       }
     })
     .process('', (error, file) => {
       t.deepEqual(
-        [error].concat(file.messages.map((m) => String(m))),
+        [error, ...file.messages.map((m) => String(m))],
         [null, '1:1: Error'],
         'should not fail when there are messages but no `children` on `tree`'
       )
diff --git a/tsconfig.json b/tsconfig.json
index 3d21d61..e31adf8 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,10 +1,16 @@
 {
+  "include": ["*.js"],
   "compilerOptions": {
-    "lib": ["es2015"],
-    "strict": true,
-    "baseUrl": ".",
-    "paths": {
-      "unified-message-control": ["."]
-    }
+    "target": "ES2020",
+    "lib": ["ES2020"],
+    "module": "ES2020",
+    "moduleResolution": "node",
+    "allowJs": true,
+    "checkJs": true,
+    "declaration": true,
+    "emitDeclarationOnly": true,
+    "allowSyntheticDefaultImports": true,
+    "skipLibCheck": true,
+    "strict": true
   }
 }
diff --git a/tslint.json b/tslint.json
deleted file mode 100644
index e339e79..0000000
--- a/tslint.json
+++ /dev/null
@@ -1,8 +0,0 @@
-{
-  "extends": "dtslint/dtslint.json",
-  "rules": {
-    "semicolon": false,
-    "whitespace": false,
-    "no-unnecessary-generics": false
-  }
-}
diff --git a/type-test.ts b/type-test.ts
deleted file mode 100644
index ce69923..0000000
--- a/type-test.ts
+++ /dev/null
@@ -1,190 +0,0 @@
-/**
- * This file is purely for typechecking and does not produce code
- */
-
-/* eslint-disable-next-line import/no-extraneous-dependencies */
-import * as control from 'unified-message-control'
-import * as unified from 'unified'
-import {Node} from 'unist'
-import {HTML} from 'mdast'
-import {Element} from 'hast'
-
-// $ExpectError
-control({})
-
-control({
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html'
-})
-
-control({
-  name: 'foo',
-  marker: (n: Node) => ({
-    name: 'foo',
-    attributes: 'bar=false',
-    parameters: {
-      bar: false
-    },
-    node: {
-      type: 'foo',
-      value: 'bar=false'
-    }
-  }),
-  test: 'foo'
-})
-
-control({
-  name: 'foo',
-  marker: (n: Element) => null,
-  test: 'element'
-})
-
-control({
-  name: 'foo',
-  marker: (n: HTML) => null,
-  test: 'html'
-})
-
-control({
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  known: ['rule-1', 'rule-2']
-})
-
-control({
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  sources: 'example'
-})
-
-control({
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  sources: ['one', 'two']
-})
-
-control({
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  reset: false,
-  disable: ['rule-id']
-})
-
-// prettier-ignore
-control({
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  reset: false, enable: ['rule-id'] // $ExpectError
-})
-
-control({
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  reset: true,
-  enable: ['rule-id']
-})
-
-// prettier-ignore
-control({
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  reset: true, disable: ['rule-id'] // $ExpectError
-})
-
-// $ExpectError
-unified().use(control, {})
-
-unified().use(control, {
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html'
-})
-
-unified().use(control, {
-  name: 'foo',
-  marker: (n: Node) => ({
-    name: 'foo',
-    attributes: 'bar=false',
-    parameters: {
-      bar: false
-    },
-    node: {
-      type: 'foo',
-      value: 'bar=false'
-    }
-  }),
-  test: 'foo'
-})
-
-unified().use(control, {
-  name: 'foo',
-  marker: (n: Element) => null,
-  test: 'element'
-})
-
-unified().use(control, {
-  name: 'foo',
-  marker: (n: HTML) => null,
-  test: 'html'
-})
-
-unified().use(control, {
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  known: ['rule-1', 'rule-2']
-})
-
-unified().use(control, {
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  sources: 'example'
-})
-
-unified().use(control, {
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  sources: ['one', 'two']
-})
-
-unified().use(control, {
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  reset: false,
-  disable: ['rule-id']
-})
-
-// prettier-ignore
-unified().use(control, {
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  reset: false, enable: ['rule-id'] // $ExpectError
-})
-
-unified().use(control, {
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  reset: true,
-  enable: ['rule-id']
-})
-
-// prettier-ignore
-unified().use(control, {
-  name: 'foo',
-  marker: (n: Node) => null,
-  test: 'html',
-  reset: true, disable: ['rule-id'] // $ExpectError
-})