diff --git a/index.js b/index.js
index f6d721a..20d2020 100644
--- a/index.js
+++ b/index.js
@@ -1,60 +1,6 @@
 /**
- * @typedef {import('unist').Node} Node
- * @typedef {import('unist').Parent} Parent
- * @typedef {import('unist').Literal} Literal
- * @typedef {Record<string, unknown>} Props
- * @typedef {Array<Node>|string} ChildrenOrValue
- *
- * @typedef {(<T extends string, P extends Record<string, unknown>, C extends Array<Node>>(type: T, props: P, children: C) => {type: T, children: C} & P)} BuildParentWithProps
- * @typedef {(<T extends string, P extends Record<string, unknown>>(type: T, props: P, value: string) => {type: T, value: string} & P)} BuildLiteralWithProps
- * @typedef {(<T extends string, P extends Record<string, unknown>>(type: T, props: P) => {type: T} & P)} BuildVoidWithProps
- * @typedef {(<T extends string, C extends Array<Node>>(type: T, children: C) => {type: T, children: C})} BuildParent
- * @typedef {(<T extends string>(type: T, value: string) => {type: T, value: string})} BuildLiteral
- * @typedef {(<T extends string>(type: T) => {type: T})} BuildVoid
+ * @typedef {import('./lib/index.js').Props} Props
+ * @typedef {import('./lib/index.js').ChildrenOrValue} ChildrenOrValue
  */
 
-/**
- * Build a node.
- *
- * @param type
- *   Node type.
- * @param [props]
- *   Fields assigned to node.
- * @param [value]
- *   Children of node or value of `node` (cast to string).
- * @returns
- *   Built node.
- */
-export const u = /**
- * @type {BuildVoid & BuildVoidWithProps & BuildLiteral & BuildLiteralWithProps & BuildParent & BuildParentWithProps}
- */ (
-  /**
-   * @param {string} type
-   * @param {Props|ChildrenOrValue} [props]
-   * @param {ChildrenOrValue} [value]
-   * @returns {Node}
-   */
-  function (type, props, value) {
-    /** @type {Node} */
-    const node = {type: String(type)}
-
-    if (
-      (value === undefined || value === null) &&
-      (typeof props === 'string' || Array.isArray(props))
-    ) {
-      value = props
-    } else {
-      Object.assign(node, props)
-    }
-
-    if (Array.isArray(value)) {
-      // @ts-expect-error: create a parent.
-      node.children = value
-    } else if (value !== undefined && value !== null) {
-      // @ts-expect-error: create a literal.
-      node.value = String(value)
-    }
-
-    return node
-  }
-)
+export {u} from './lib/index.js'
diff --git a/lib/index.js b/lib/index.js
new file mode 100644
index 0000000..f6d721a
--- /dev/null
+++ b/lib/index.js
@@ -0,0 +1,60 @@
+/**
+ * @typedef {import('unist').Node} Node
+ * @typedef {import('unist').Parent} Parent
+ * @typedef {import('unist').Literal} Literal
+ * @typedef {Record<string, unknown>} Props
+ * @typedef {Array<Node>|string} ChildrenOrValue
+ *
+ * @typedef {(<T extends string, P extends Record<string, unknown>, C extends Array<Node>>(type: T, props: P, children: C) => {type: T, children: C} & P)} BuildParentWithProps
+ * @typedef {(<T extends string, P extends Record<string, unknown>>(type: T, props: P, value: string) => {type: T, value: string} & P)} BuildLiteralWithProps
+ * @typedef {(<T extends string, P extends Record<string, unknown>>(type: T, props: P) => {type: T} & P)} BuildVoidWithProps
+ * @typedef {(<T extends string, C extends Array<Node>>(type: T, children: C) => {type: T, children: C})} BuildParent
+ * @typedef {(<T extends string>(type: T, value: string) => {type: T, value: string})} BuildLiteral
+ * @typedef {(<T extends string>(type: T) => {type: T})} BuildVoid
+ */
+
+/**
+ * Build a node.
+ *
+ * @param type
+ *   Node type.
+ * @param [props]
+ *   Fields assigned to node.
+ * @param [value]
+ *   Children of node or value of `node` (cast to string).
+ * @returns
+ *   Built node.
+ */
+export const u = /**
+ * @type {BuildVoid & BuildVoidWithProps & BuildLiteral & BuildLiteralWithProps & BuildParent & BuildParentWithProps}
+ */ (
+  /**
+   * @param {string} type
+   * @param {Props|ChildrenOrValue} [props]
+   * @param {ChildrenOrValue} [value]
+   * @returns {Node}
+   */
+  function (type, props, value) {
+    /** @type {Node} */
+    const node = {type: String(type)}
+
+    if (
+      (value === undefined || value === null) &&
+      (typeof props === 'string' || Array.isArray(props))
+    ) {
+      value = props
+    } else {
+      Object.assign(node, props)
+    }
+
+    if (Array.isArray(value)) {
+      // @ts-expect-error: create a parent.
+      node.children = value
+    } else if (value !== undefined && value !== null) {
+      // @ts-expect-error: create a literal.
+      node.value = String(value)
+    }
+
+    return node
+  }
+)
diff --git a/package.json b/package.json
index d41d779..a11b699 100644
--- a/package.json
+++ b/package.json
@@ -35,6 +35,7 @@
   "main": "index.js",
   "types": "index.d.ts",
   "files": [
+    "lib/",
     "index.d.ts",
     "index.js"
   ],