diff --git a/index.js b/index.js
index b382033..bce534d 100644
--- a/index.js
+++ b/index.js
@@ -1,11 +1,13 @@
 /**
  * @typedef {import('unist').Position} Position
  * @typedef {import('unist').Node} Node
- * @typedef {Record<string, unknown> & {type: string, position?: Position|undefined}} NodeLike
+ * @typedef {import('./lib/types.js').SelectState} SelectState
+ * @typedef {Record<string, unknown> & {type: string, position?: Position | undefined}} NodeLike
  */
 
 import {any} from './lib/any.js'
 import {parse} from './lib/parse.js'
+import {root} from './lib/util.js'
 
 /**
  * Check that the given `node` matches `selector`.
@@ -17,13 +19,17 @@ import {parse} from './lib/parse.js'
  *
  * @param {string} selector
  *   CSS selector, such as (`heading`, `link, linkReference`).
- * @param {Node | NodeLike | undefined} [node]
+ * @param {Node | NodeLike | null | undefined} [node]
  *   Node that might match `selector`.
  * @returns {boolean}
  *   Whether `node` matches `selector`.
  */
 export function matches(selector, node) {
-  return Boolean(any(parse(selector), node, {one: true, shallow: true, any})[0])
+  const state = createState(node)
+  state.one = true
+  state.shallow = true
+  const result = any(parse(selector), node || undefined, state)
+  return result.length > 0
 }
 
 /**
@@ -33,7 +39,7 @@ export function matches(selector, node) {
  *
  * @param {string} selector
  *   CSS selector, such as (`heading`, `link, linkReference`).
- * @param {Node | NodeLike | undefined} [tree]
+ * @param {Node | NodeLike | null | undefined} [tree]
  *   Tree to search.
  * @returns {Node | null}
  *   First node in `tree` that matches `selector` or `null` if nothing is
@@ -42,7 +48,11 @@ export function matches(selector, node) {
  *   This could be `tree` itself.
  */
 export function select(selector, tree) {
-  return any(parse(selector), tree, {one: true, any})[0] || null
+  const state = createState(tree)
+  state.one = true
+  const result = any(parse(selector), tree || undefined, state)
+  // To do next major: return `undefined`.
+  return result[0] || null
 }
 
 /**
@@ -52,7 +62,7 @@ export function select(selector, tree) {
  *
  * @param {string} selector
  *   CSS selector, such as (`heading`, `link, linkReference`).
- * @param {Node | NodeLike | undefined} [tree]
+ * @param {Node | NodeLike | null | undefined} [tree]
  *   Tree to search.
  * @returns {Array<Node>}
  *   Nodes in `tree` that match `selector`.
@@ -60,5 +70,26 @@ export function select(selector, tree) {
  *   This could include `tree` itself.
  */
 export function selectAll(selector, tree) {
-  return any(parse(selector), tree, {any})
+  const state = createState(tree)
+  return any(parse(selector), tree || undefined, state)
+}
+
+/**
+ * @param {Node | null | undefined} tree
+ * @returns {SelectState}
+ */
+function createState(tree) {
+  return {
+    any,
+    iterator: undefined,
+    scopeNodes: tree ? (root(tree) ? tree.children : [tree]) : [],
+    one: false,
+    shallow: false,
+    index: false,
+    found: false,
+    typeIndex: undefined,
+    nodeIndex: undefined,
+    typeCount: undefined,
+    nodeCount: undefined
+  }
 }
diff --git a/lib/any.js b/lib/any.js
index eb45886..662e487 100644
--- a/lib/any.js
+++ b/lib/any.js
@@ -22,10 +22,10 @@ const type = zwitch('type', {
 })
 
 /**
- * @param {Selectors|RuleSet|Rule} query
- * @param {Node|undefined} node
+ * @param {Selectors | RuleSet | Rule} query
+ * @param {Node | undefined} node
  * @param {SelectState} state
- * @returns {Array.<Node>}
+ * @returns {Array<Node>}
  */
 export function any(query, node, state) {
   // @ts-expect-error: fine.
@@ -73,7 +73,7 @@ function rule(query, tree, state) {
     query,
     tree,
     0,
-    null,
+    undefined,
     configure(query, {
       any: state.any,
       iterator,
@@ -124,7 +124,7 @@ function configure(query, state) {
   return state
 }
 
-// Shouldn’t be invoked, all data is handled.
+// Shouldn’t be called, all data is handled.
 /* c8 ignore next 6 */
 /**
  * @param {{[x: string]: unknown, type: string}} query
@@ -133,17 +133,17 @@ function unknownType(query) {
   throw new Error('Unknown type `' + query.type + '`')
 }
 
-// Shouldn’t be invoked, parser gives correct data.
+// Shouldn’t be called, parser gives correct data.
 /* c8 ignore next 3 */
 function invalidType() {
   throw new Error('Invalid type')
 }
 
 /**
- * @param {boolean|undefined} one
+ * @param {boolean | undefined} one
  */
 function collector(one) {
-  /** @type {Array.<Node>} */
+  /** @type {Array<Node>} */
   const result = []
   /** @type {boolean} */
   let found
@@ -155,7 +155,7 @@ function collector(one) {
   /**
    * Append nodes to array, filtering out duplicates.
    *
-   * @param {Node|Array.<Node>} node
+   * @param {Node | Array<Node>} node
    */
   function collect(node) {
     let index = -1
diff --git a/lib/attribute.js b/lib/attribute.js
index ec9f173..5a14c39 100644
--- a/lib/attribute.js
+++ b/lib/attribute.js
@@ -76,7 +76,7 @@ function containsArray(query, node) {
 
   // If this is an array, and the query is contained in it, return true.
   // Coverage comment in place because TS turns `Array.isArray(unknown)`
-  // into `Array.<any>` instead of `Array.<unknown>`.
+  // into `Array<any>` instead of `Array<unknown>`.
   // type-coverage:ignore-next-line
   if (Array.isArray(value) && value.includes(query.value)) {
     return true
@@ -135,7 +135,7 @@ function containsString(query, node) {
   return query.value && typeof value === 'string' && value.includes(query.value)
 }
 
-// Shouldn’t be invoked, Parser throws an error instead.
+// Shouldn’t be called, parser throws an error instead.
 /* c8 ignore next 6 */
 /**
  * @param {{[x: string]: unknown, type: string}} query
diff --git a/lib/nest.js b/lib/nest.js
index 5ddf556..0cb406b 100644
--- a/lib/nest.js
+++ b/lib/nest.js
@@ -32,7 +32,7 @@ const handle = zwitch('nestingOperator', {
 /** @type {Handler} */
 export const nest = handle
 
-// Shouldn’t be invoked, parser gives correct data.
+// Shouldn’t be called, parser gives correct data.
 /* c8 ignore next 6 */
 /**
  * @param {{[x: string]: unknown, type: string}} query
@@ -93,7 +93,7 @@ function child(query, node, _1, _2, state) {
   if (!parent(node)) return
   if (node.children.length === 0) return
 
-  new WalkIterator(query, node, state).each().done()
+  new WalkIterator(query, node, state).each(undefined, undefined).done()
 }
 
 /** @type {Handler} */
@@ -111,7 +111,7 @@ function adjacentSibling(query, _, index, parent, state) {
   new WalkIterator(query, parent, state)
     .prefillTypeIndex(0, ++index)
     .each(index, ++index)
-    .prefillTypeIndex(index)
+    .prefillTypeIndex(index, undefined)
     .done()
 }
 
@@ -129,7 +129,7 @@ function generalSibling(query, _, index, parent, state) {
 
   new WalkIterator(query, parent, state)
     .prefillTypeIndex(0, ++index)
-    .each(index)
+    .each(index, undefined)
     .done()
 }
 
@@ -148,15 +148,15 @@ class WalkIterator {
     this.parent = parent
     /** @type {SelectState} */
     this.state = state
-    /** @type {TypeIndex|undefined} */
+    /** @type {TypeIndex | undefined} */
     this.typeIndex = state.index ? new TypeIndex() : undefined
-    /** @type {Array.<Function>} */
+    /** @type {Array<Function>} */
     this.delayed = []
   }
 
   /**
-   * @param {number|null|undefined} [x]
-   * @param {number|null|undefined} [y]
+   * @param {number | undefined} x
+   * @param {number | undefined} y
    * @returns {this}
    */
   prefillTypeIndex(x, y) {
@@ -173,8 +173,8 @@ class WalkIterator {
   }
 
   /**
-   * @param {number|null|undefined} [x]
-   * @param {number|null|undefined} [y]
+   * @param {number | undefined} x
+   * @param {number | undefined} y
    * @returns {this}
    */
   each(x, y) {
@@ -246,13 +246,13 @@ class WalkIterator {
   }
 
   /**
-   * @param {number|null|undefined} [start]
-   * @param {number|null|undefined} [end]
+   * @param {number | undefined} start
+   * @param {number | undefined} end
    * @returns {[number, number]}
    */
   defaults(start, end) {
-    if (start === null || start === undefined || start < 0) start = 0
-    if (end === null || end === undefined || end > this.parent.children.length)
+    if (start === undefined || start < 0) start = 0
+    if (end === undefined || end > this.parent.children.length)
       end = this.parent.children.length
     return [start, end]
   }
@@ -260,7 +260,7 @@ class WalkIterator {
 
 class TypeIndex {
   constructor() {
-    /** @type {Object.<string, number>} */
+    /** @type {Record<string, number>} */
     this.counts = {}
     /** @type {number} */
     this.nodes = 0
@@ -283,7 +283,7 @@ class TypeIndex {
 
   /**
    * @param {Node} node
-   * @returns {number|undefined}
+   * @returns {number | undefined}
    */
   count(node) {
     return this.counts[node.type]
diff --git a/lib/parse.js b/lib/parse.js
index 95ec356..42cf111 100644
--- a/lib/parse.js
+++ b/lib/parse.js
@@ -70,7 +70,7 @@ function ruleSet(query) {
 function rule(query) {
   const pseudos = query.pseudos || []
   let index = -1
-  /** @type {RulePseudo|RulePseudoNth} */
+  /** @type {RulePseudo | RulePseudoNth} */
   let pseudo
 
   while (++index < pseudos.length) {
diff --git a/lib/pseudo.js b/lib/pseudo.js
index 16f2992..33b834d 100644
--- a/lib/pseudo.js
+++ b/lib/pseudo.js
@@ -79,8 +79,8 @@ pseudo.needsIndex = [
 /**
  * @param {Rule} query
  * @param {Node} node
- * @param {number|null} index
- * @param {Parent|null} parent
+ * @param {number | undefined} index
+ * @param {Parent | undefined} parent
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -98,8 +98,8 @@ export function pseudo(query, node, index, parent, state) {
 /**
  * @param {RulePseudoSelector} query
  * @param {Node} node
- * @param {number|null} _1
- * @param {Parent|null} _2
+ * @param {number | undefined} _1
+ * @param {Parent | undefined} _2
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -121,8 +121,8 @@ function matches(query, node, _1, _2, state) {
 /**
  * @param {RulePseudoSelector} query
  * @param {Node} node
- * @param {number|null} index
- * @param {Parent|null} parent
+ * @param {number | undefined} index
+ * @param {Parent | undefined} parent
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -133,8 +133,8 @@ function not(query, node, index, parent, state) {
 /**
  * @param {RulePseudo} _1
  * @param {Node} node
- * @param {number|null} _2
- * @param {Parent|null} parent
+ * @param {number | undefined} _2
+ * @param {Parent | undefined} parent
  * @returns {boolean}
  */
 function root(_1, node, _2, parent) {
@@ -144,8 +144,8 @@ function root(_1, node, _2, parent) {
 /**
  * @param {RulePseudo} _1
  * @param {Node} node
- * @param {number|null} _2
- * @param {Parent|null} _3
+ * @param {number | undefined} _2
+ * @param {Parent | undefined} _3
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -169,8 +169,8 @@ function empty(_1, node) {
 /**
  * @param {RulePseudo} query
  * @param {Node} _1
- * @param {number|null} _2
- * @param {Parent|null} _3
+ * @param {number | undefined} _2
+ * @param {Parent | undefined} _3
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -182,8 +182,8 @@ function firstChild(query, _1, _2, _3, state) {
 /**
  * @param {RulePseudo} query
  * @param {Node} _1
- * @param {number|null} _2
- * @param {Parent|null} _3
+ * @param {number | undefined} _2
+ * @param {Parent | undefined} _3
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -198,8 +198,8 @@ function lastChild(query, _1, _2, _3, state) {
 /**
  * @param {RulePseudo} query
  * @param {Node} _1
- * @param {number|null} _2
- * @param {Parent|null} _3
+ * @param {number | undefined} _2
+ * @param {Parent | undefined} _3
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -211,8 +211,8 @@ function onlyChild(query, _1, _2, _3, state) {
 /**
  * @param {RulePseudoNth} query
  * @param {Node} _1
- * @param {number|null} _2
- * @param {Parent|null} _3
+ * @param {number | undefined} _2
+ * @param {Parent | undefined} _3
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -224,8 +224,8 @@ function nthChild(query, _1, _2, _3, state) {
 /**
  * @param {RulePseudoNth} query
  * @param {Node} _1
- * @param {number|null} _2
- * @param {Parent|null} _3
+ * @param {number | undefined} _2
+ * @param {Parent | undefined} _3
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -241,8 +241,8 @@ function nthLastChild(query, _1, _2, _3, state) {
 /**
  * @param {RulePseudoNth} query
  * @param {Node} _1
- * @param {number|null} _2
- * @param {Parent|null} _3
+ * @param {number | undefined} _2
+ * @param {Parent | undefined} _3
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -254,8 +254,8 @@ function nthOfType(query, _1, _2, _3, state) {
 /**
  * @param {RulePseudoNth} query
  * @param {Node} _1
- * @param {number|null} _2
- * @param {Parent|null} _3
+ * @param {number | undefined} _2
+ * @param {Parent | undefined} _3
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -271,8 +271,8 @@ function nthLastOfType(query, _1, _2, _3, state) {
 /**
  * @param {RulePseudo} query
  * @param {Node} _1
- * @param {number|null} _2
- * @param {Parent|null} _3
+ * @param {number | undefined} _2
+ * @param {Parent | undefined} _3
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -284,8 +284,8 @@ function firstOfType(query, _1, _2, _3, state) {
 /**
  * @param {RulePseudo} query
  * @param {Node} _1
- * @param {number|null} _2
- * @param {Parent|null} _3
+ * @param {number | undefined} _2
+ * @param {Parent | undefined} _3
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -300,8 +300,8 @@ function lastOfType(query, _1, _2, _3, state) {
 /**
  * @param {RulePseudo} query
  * @param {Node} _1
- * @param {number|null} _2
- * @param {Parent|null} _3
+ * @param {number | undefined} _2
+ * @param {Parent | undefined} _3
  * @param {SelectState} state
  * @returns {boolean}
  */
@@ -310,7 +310,7 @@ function onlyOfType(query, _1, _2, _3, state) {
   return state.typeCount === 1
 }
 
-// Shouldn’t be invoked, parser gives correct data.
+// Shouldn’t be called, parser gives correct data.
 /* c8 ignore next 3 */
 function invalidPseudo() {
   throw new Error('Invalid pseudo-selector')
@@ -330,7 +330,7 @@ function unknownPseudo(query) {
 
 /**
  * @param {SelectState} state
- * @param {RulePseudo|RulePseudoNth} query
+ * @param {RulePseudo | RulePseudoNth} query
  */
 function assertDeep(state, query) {
   if (state.shallow) {
@@ -341,8 +341,8 @@ function assertDeep(state, query) {
 /**
  * @param {RulePseudoSelector} query
  * @param {Node} node
- * @param {number|null} _1
- * @param {Parent|null} _2
+ * @param {number | undefined} _1
+ * @param {Parent | undefined} _2
  * @param {SelectState} state
  * @returns {boolean}
  */
diff --git a/lib/test.js b/lib/test.js
index 18f6938..d239c22 100644
--- a/lib/test.js
+++ b/lib/test.js
@@ -12,8 +12,8 @@ import {pseudo} from './pseudo.js'
 /**
  * @param {Rule} query
  * @param {Node} node
- * @param {number|null} index
- * @param {Parent|null} parent
+ * @param {number | undefined} index
+ * @param {Parent | undefined} parent
  * @param {SelectState} state
  * @returns {boolean}
  */
diff --git a/lib/types.js b/lib/types.js
index 7ac74e7..eecd883 100644
--- a/lib/types.js
+++ b/lib/types.js
@@ -8,20 +8,27 @@
  * @typedef {import('css-selector-parser').Rule} Rule
  * @typedef {import('css-selector-parser').RulePseudo} RulePseudo
  * @typedef {import('css-selector-parser').AttrValueType} AttrValueType
- * @typedef {Selector|Rule|RulePseudo} Query
+ * @typedef {Selector | Rule | RulePseudo} Query
  *
  * @typedef RuleAttr
  *   Fix for types from `css-selector-parser`.
  * @property {string} name
- * @property {string} [operator]
- * @property {AttrValueType} [valueType]
- * @property {string} [value]
+ *   Attribute name.
+ * @property {string | undefined} [operator]
+ *   Operator, such as `'|='`, missing when for example `[x]`.
+ * @property {AttrValueType | undefined} [valueType]
+ *   Attribute value type.
+ * @property {string | undefined} [value]
+ *   Attribute value.
  *
  * @typedef RulePseudoSelector
  *   More specific type for registered selector pseudos.
  * @property {string} name
+ *   Name of pseudo, such as `'matches'`.
  * @property {'selector'} valueType
- * @property {Selector} value
+ *   Set to `'selector'`, because `value` is a compiled selector.
+ * @property {Selectors | RuleSet} value
+ *   Selector.
  *
  * @typedef RulePseudoNth
  *   Overwrite to compile nth-checks once.
@@ -30,20 +37,20 @@
  * @property {(index: number) => boolean} value
  *
  * @typedef SelectState
- * @property {(query: Selectors|RuleSet|Rule, node: Node|undefined, state: SelectState) => Node[]} any
- * @property {SelectIterator|null|undefined} [iterator]
- * @property {Array<Node>} [scopeNodes]
- * @property {boolean} [one=false]
- * @property {boolean} [shallow=false]
- * @property {boolean} [index=false]
- * @property {boolean} [found=false]
- * @property {number} [typeIndex]
+ * @property {(query: Selectors | RuleSet | Rule, node: Node | undefined, state: SelectState) => Array<Node>} any
+ * @property {SelectIterator | undefined} iterator
+ * @property {Array<Node>} scopeNodes
+ * @property {boolean} one
+ * @property {boolean} shallow
+ * @property {boolean} index
+ * @property {boolean} found
+ * @property {number | undefined} typeIndex
  *   Track siblings: this current node has `n` nodes with its type before it.
- * @property {number} [nodeIndex]
+ * @property {number | undefined} nodeIndex
  *   Track siblings: this current node has `n` nodes before it.
- * @property {number} [typeCount]
+ * @property {number | undefined} typeCount
  *   Track siblings: there are `n` siblings with this node’s type.
- * @property {number} [nodeCount]
+ * @property {number | undefined} nodeCount
  *   Track siblings: there are `n` siblings.
  */
 
@@ -52,13 +59,13 @@
  * @param {Rule} query
  * @param {Node} node
  * @param {number} index
- * @param {Parent|null} parent
+ * @param {Parent | undefined} parent
  * @param {SelectState} state
  */
 
 /**
  * @typedef {(
- *  ((query: Rule, node: Node, index: number|null, parent: Parent|null, state: SelectState) => void)
+ *  ((query: Rule, node: Node, index: number | undefined, parent: Parent | undefined, state: SelectState) => void)
  * )} Handler
  */