diff --git a/lib/index.d.ts b/lib/index.d.ts
index a6af47d..97488dd 100644
--- a/lib/index.d.ts
+++ b/lib/index.d.ts
@@ -18,17 +18,17 @@ import * as postcss from "postcss";
 
 export interface NodeBase {
   // Inherited from postcss.ContainerBase, but with our Node type.
-  next(): Node | void;
-  prev(): Node | void;
-  before(newNode: Node | object | string | Node[]): this;
-  after(newNode: Node | object | string | Node[]): this;
+  next(): ChildNode | void;
+  prev(): ChildNode | void;
+  before(newNode: ChildNode | object | string | ChildNode[]): this;
+  after(newNode: ChildNode | object | string | ChildNode[]): this;
   root(): Root;
-  replaceWith(...nodes: Array<Node | object>): this;
+  replaceWith(...nodes: Array<ChildNode | object>): this;
 
   // Inherited from postcss.ContainerBase with no changes.
   source?: postcss.NodeSource;
   raws: postcss.NodeRaws;
-  toString(stringifier?: postcss.Stringifier | postcss.Syntax): string;
+  toString(stringifier?: Stringifier | Syntax): string;
   error(
     message: string,
     options?: postcss.NodeErrorOptions
@@ -66,33 +66,39 @@ export interface ContainerBase extends NodeBase {
   walkWords(callback: (word: Word, index: number) => any): boolean | void;
   walkType(
     type: string,
-    callback: (node: Node, index: number) => any
+    callback: (node: ChildNode, index: number) => any
   ): boolean | void;
 
   // Inherited from postcss.ContainerBase, but with our Node type.
-  nodes: Node[];
-  first?: Node;
-  last?: Node;
-  index(child: Node | number): number;
+  nodes: ChildNode[];
+  first?: ChildNode;
+  last?: ChildNode;
+  index(child: ChildNode | number): number;
   every(
-    callback: (node: Node, index: number, nodes: Node[]) => any,
+    callback: (node: ChildNode, index: number, nodes: ChildNode[]) => any,
     thisArg?: any
   ): boolean;
   some(
-    callback: (node: Node, index: number, nodes: Node[]) => boolean,
+    callback: (node: ChildNode, index: number, nodes: ChildNode[]) => boolean,
     thisArg?: any
   ): boolean;
-  each(callback: (node: Node, index: number) => any): boolean | void;
-  walk(callback: (node: Node, index: number) => any): boolean | void;
+  each(callback: (node: ChildNode, index: number) => any): boolean | void;
+  walk(callback: (node: ChildNode, index: number) => any): boolean | void;
   walkAtWords(callback: (atWord: AtWord, index: number) => any): boolean | void;
   walkComments(
     callback: (comment: Comment, index: number) => any
   ): boolean | void;
-  prepend(...nodes: Array<Node | object | string>): this;
-  append(...nodes: Array<Node | object | string>): this;
-  insertBefore(oldNode: Node | number, newNode: Node | object | string): this;
-  insertAfter(oldNode: Node | number, newNode: Node | object | string): this;
-  removeChild(child: Node | number): this;
+  prepend(...nodes: Array<ChildNode | object | string>): this;
+  append(...nodes: Array<ChildNode | object | string>): this;
+  insertBefore(
+    oldNode: ChildNode | number,
+    newNode: ChildNode | object | string
+  ): this;
+  insertAfter(
+    oldNode: ChildNode | number,
+    newNode: ChildNode | object | string
+  ): this;
+  removeChild(child: ChildNode | number): this;
 
   // Inherited from postcss.ContainerBase with no changes.
   clone(overrides?: object): this;
@@ -109,7 +115,9 @@ export interface Root extends ContainerBase {
   }): postcss.Result;
 }
 
-export type Node =
+export type Node = Root | ChildNode;
+
+export type ChildNode =
   | AtWord
   | Comment
   | Func
@@ -121,7 +129,7 @@ export type Node =
   | UnicodeRange
   | Word;
 
-export type Container = Func | Interpolation;
+export type Container = Root | Func | Interpolation;
 
 export interface AtWord extends NodeBase {
   type: "atrule";
@@ -141,6 +149,7 @@ export interface Func extends ContainerBase {
   type: "func";
   parent: Container;
   isColor: boolean;
+  isVar: boolean;
   name: string;
   params: string;
 }
@@ -210,6 +219,18 @@ export interface VariablesOptions {
   prefixes: string[];
 }
 
-export const stringify: postcss.Stringifier;
+interface Syntax {
+  stringify?: Stringifier;
+}
+
+interface Builder {
+  (part: string, node?: Node, type?: "start" | "end"): void;
+}
+
+export interface Stringifier {
+  (node: Node, builder: Builder): void;
+}
+
+export const stringify: Stringifier;
 
 export function nodeToString(node: Node): string;