diff --git a/.changeset/loud-dragons-provide.md b/.changeset/loud-dragons-provide.md
new file mode 100644
index 0000000..62ca4b7
--- /dev/null
+++ b/.changeset/loud-dragons-provide.md
@@ -0,0 +1,5 @@
+---
+"@udt/parser-utils": minor
+---
+
+BREAKING CHANGE: `ParseGroupDataFn` can no longer return an `addChild` function. Instead, you should now provide an `addChildToGroup` function in your parser config.
diff --git a/.changeset/slow-insects-marry.md b/.changeset/slow-insects-marry.md
new file mode 100644
index 0000000..04bc3bf
--- /dev/null
+++ b/.changeset/slow-insects-marry.md
@@ -0,0 +1,5 @@
+---
+"@udt/parser-utils": minor
+---
+
+BREAKING CHANGE: `parseData()` may now return `undefined` (happens if no `parseGroupData` function is set in the config).
diff --git a/.changeset/tidy-islands-punch.md b/.changeset/tidy-islands-punch.md
new file mode 100644
index 0000000..99323df
--- /dev/null
+++ b/.changeset/tidy-islands-punch.md
@@ -0,0 +1,5 @@
+---
+"@udt/parser-utils": minor
+---
+
+BREAKING CHANGE: `extractProperties()` now returns an object containing unextract properties and their values, instead of an array of unextracted property names.
diff --git a/packages/demos/src/simple-dtcg-parser.ts b/packages/demos/src/simple-dtcg-parser.ts
index d688e68..e066ead 100644
--- a/packages/demos/src/simple-dtcg-parser.ts
+++ b/packages/demos/src/simple-dtcg-parser.ts
@@ -71,7 +71,6 @@ export function parseDtcg(data: unknown) {
     }
 
     return {
-      group: undefined,
       contextForChildren,
     };
   }
diff --git a/packages/dtcg-parser/src/parse-dtcg-file-data.ts b/packages/dtcg-parser/src/parse-dtcg-file-data.ts
index b27fdc2..287ebd4 100644
--- a/packages/dtcg-parser/src/parse-dtcg-file-data.ts
+++ b/packages/dtcg-parser/src/parse-dtcg-file-data.ts
@@ -21,6 +21,9 @@ export function parseDtcgFileData(dtcgData: unknown): RootGroup {
     groupPropsToExtract: [dtcgPropRegex],
     parseGroupData: parseGroup,
     parseDesignTokenData: parseToken,
+    addChildToGroup(group, _name, child) {
+      group.addChild(child);
+    },
   });
 
   if (!(result instanceof RootGroup)) {
diff --git a/packages/dtcg-parser/src/parse-group.ts b/packages/dtcg-parser/src/parse-group.ts
index 1503e6f..c66a24d 100644
--- a/packages/dtcg-parser/src/parse-group.ts
+++ b/packages/dtcg-parser/src/parse-group.ts
@@ -1,11 +1,11 @@
-import { type DesignToken, Group, RootGroup } from "@udt/tom";
+import { Group, RootGroup } from "@udt/tom";
 import { type PlainObject, type ParseGroupResult } from "@udt/parser-utils";
 import { extractCommonProps } from "./extract-common-props.js";
 
 export function parseGroup(
   groupProps: PlainObject,
   path: string[]
-): ParseGroupResult<Group | RootGroup, DesignToken, never> {
+): ParseGroupResult<Group | RootGroup, never> {
   const { commonProps, rest } = extractCommonProps(groupProps);
 
   if (Object.keys(rest).length > 0) {
@@ -22,8 +22,5 @@ export function parseGroup(
 
   return {
     group,
-    addChild(_name, child: Group | DesignToken) {
-      group.addChild(child);
-    },
   };
 }
diff --git a/packages/parser-utils/README.md b/packages/parser-utils/README.md
index 2f6a264..22cb35b 100644
--- a/packages/parser-utils/README.md
+++ b/packages/parser-utils/README.md
@@ -39,7 +39,18 @@ const parsedData = parseData(fileData, {
   // format properties
   groupPropsToExtract: [ /* ... */ ];
 
-  // Function which is called for each group data object
+  // Function which is called for each design token
+  // data object that is encountered.
+  //
+  // Is given the design token data and its path, and
+  // should parse that data into whatever structure is
+  // desired.
+  parseDesignTokenData: (data, path, contextFromParent) => {
+    /* ... */
+    return parsedDesignToken;
+  },
+
+  // OPTIONAL function which is called for each group data object
   // that is encountered.
   //
   // Is given the extracted properties of that group and its
@@ -50,24 +61,17 @@ const parsedData = parseData(fileData, {
     return {
       group: parsedGroup,
 
-      // optional:
-      addChild: (childName, childGroupOrToken) => { /*... */ },
-
-      // optional:
+      // OPTIONAL:
       contextForChildren: /* anything you like */,
     }
   },
 
-  // Function which is called for each design token
-  // data object that is encountered.
+  // OPTIONAL function which is called for each design token and/or
+  // nested group found within a group.
   //
-  // Is given the design token data and its path, and
-  // should parse that data into whatever structure is
-  // desired.
-  parseDesignTokenData: (data, path, contextFromParent) => {
-    /* ... */
-    return parsedDesignToken;
-  },
+  // Useful if your parsed groups and design tokens need to be assembled into
+  // a tree structure.
+  addChildToGroup: (parsedParentGroup, childName, parsedChildGroupOrToken) => { /*... */ },
 });
 ```
 
diff --git a/packages/parser-utils/src/extractProperties.test.ts b/packages/parser-utils/src/extractProperties.test.ts
index 184aa74..46ab8b0 100644
--- a/packages/parser-utils/src/extractProperties.test.ts
+++ b/packages/parser-utils/src/extractProperties.test.ts
@@ -18,12 +18,12 @@ describe("extractProperties()", () => {
     expect(extractResult.extracted).toStrictEqual({ bar: 13, baz: 666 });
   });
 
-  it("returns keys of non-extracted properties", () => {
+  it("returns non-extracted properties", () => {
     const extractResult = extractProperties(
       { foo: 42, bar: 13, baz: 666, quux: 0 },
       ["foo", "baz"]
     );
-    expect(extractResult.remainingProps).toStrictEqual(["bar", "quux"]);
+    expect(extractResult.rest).toStrictEqual({ bar: 13, quux: 0 });
   });
 
   it("ignores props to extract that are not present in input object", () => {
diff --git a/packages/parser-utils/src/extractProperties.ts b/packages/parser-utils/src/extractProperties.ts
index 6cb5d80..f160b40 100644
--- a/packages/parser-utils/src/extractProperties.ts
+++ b/packages/parser-utils/src/extractProperties.ts
@@ -19,7 +19,7 @@ import { type PlainObject } from "./isJsonObject.js";
  */
 export function extractProperties(
   object: PlainObject,
-  propsToExtract: (string | RegExp)[]
+  propsToExtract: readonly (string | RegExp)[]
 ): {
   /**
    * Object containg the extract properties
@@ -28,10 +28,10 @@ export function extractProperties(
   extracted: PlainObject;
 
   /**
-   * Array of property names of the input
-   * object that were not extracted.
+   * Object containing the remaining, unextracted
+   * properties and their respective values.
    */
-  remainingProps: string[];
+  rest: PlainObject;
 } {
   const propNamesToExtract = propsToExtract.filter(
     (prop) => typeof prop === "string"
@@ -41,7 +41,7 @@ export function extractProperties(
   );
 
   const extracted: PlainObject = {};
-  const remainingProps: string[] = [];
+  const rest: PlainObject = {};
   Object.getOwnPropertyNames(object).forEach((prop) => {
     if (
       propNamesToExtract.some(
@@ -53,12 +53,12 @@ export function extractProperties(
     ) {
       extracted[prop] = object[prop];
     } else {
-      remainingProps.push(prop);
+      rest[prop] = object[prop];
     }
   });
 
   return {
     extracted,
-    remainingProps,
+    rest,
   };
 }
diff --git a/packages/parser-utils/src/index.ts b/packages/parser-utils/src/index.ts
index c9fb641..d5abfad 100644
--- a/packages/parser-utils/src/index.ts
+++ b/packages/parser-utils/src/index.ts
@@ -1,3 +1,5 @@
+/* v8 ignore start */
 export * from "./parseData.js";
 export * from "./isJsonObject.js";
 export * from "./extractProperties.js";
+/* v8 ignore end */
diff --git a/packages/parser-utils/src/parseData.test.ts b/packages/parser-utils/src/parseData.test.ts
index 7fcf06c..aebbcaf 100644
--- a/packages/parser-utils/src/parseData.test.ts
+++ b/packages/parser-utils/src/parseData.test.ts
@@ -19,10 +19,6 @@ interface TestDesignToken {
 
 interface TestParentContext {
   dummyData?: number;
-
-  // Used to pass in a mock addChild() function for
-  // mockParseGroupData() to use for testing
-  addChild?: AddChildFn<TestGroup, TestDesignToken>;
 }
 
 interface ParseDataCall {
@@ -53,7 +49,7 @@ const mockIsDesignTokenData = vi.fn<IsDesignTokenDataFn>(
 );
 
 const mockParseGroupData = vi.fn<
-  ParseGroupDataFn<TestGroup, TestDesignToken, TestParentContext>
+  ParseGroupDataFn<TestGroup, TestParentContext>
 >((_data, path, contextFromParent) => {
   parseDataCalls.push({
     type: "group",
@@ -65,12 +61,18 @@ const mockParseGroupData = vi.fn<
     },
     // pass through contextFromParent
     contextForChildren: contextFromParent,
-
-    // pass through addChild
-    addChild: contextFromParent?.addChild,
   };
 });
 
+const mockAddChildToGroup = vi.fn<AddChildFn<TestGroup, TestDesignToken>>(
+  (_parent, name, _child) => {
+    parseDataCalls.push({
+      type: "addChild",
+      name,
+    });
+  }
+);
+
 const mockParseDesignTokenData = vi.fn<
   ParseDesignTokenDataFn<TestDesignToken, TestParentContext>
 >((_data, path, _contextFromParent) => {
@@ -81,20 +83,23 @@ const mockParseDesignTokenData = vi.fn<
   return result;
 });
 
+const defaultParserConfig: ParserConfig<
+  TestDesignToken,
+  TestGroup,
+  TestParentContext
+> = {
+  isDesignTokenData: mockIsDesignTokenData,
+  groupPropsToExtract: [],
+  parseGroupData: mockParseGroupData,
+  parseDesignTokenData: mockParseDesignTokenData,
+};
+
 describe("parseData()", () => {
-  const parserConfig: ParserConfig<
-    TestDesignToken,
-    TestGroup,
-    TestParentContext
-  > = {
-    isDesignTokenData: mockIsDesignTokenData,
-    groupPropsToExtract: [],
-    parseGroupData: mockParseGroupData,
-    parseDesignTokenData: mockParseDesignTokenData,
-  };
+  let parserConfig: ParserConfig<TestDesignToken, TestGroup, TestParentContext>;
 
   beforeEach(() => {
     // Reset stuff
+    parserConfig = defaultParserConfig;
     parseDataCalls = [];
     parserConfig.groupPropsToExtract = [];
     mockIsDesignTokenData.mockClear();
@@ -103,14 +108,14 @@ describe("parseData()", () => {
   });
 
   describe("parsing an empty group object", () => {
-    let parsedGroupOrToken: TestGroup | TestDesignToken;
+    let parsedGroupOrToken: TestGroup | TestDesignToken | undefined;
 
     beforeEach(() => {
       parsedGroupOrToken = parseData({}, parserConfig);
     });
 
     it("returns a group", () => {
-      expect(parsedGroupOrToken.type).toBe("group");
+      expect(parsedGroupOrToken?.type).toBe("group");
     });
 
     it("calls isDesignTokenData function once", () => {
@@ -141,14 +146,14 @@ describe("parseData()", () => {
       stuff: 123,
       notAGroup: {},
     };
-    let parsedGroupOrToken: TestGroup | TestDesignToken;
+    let parsedGroupOrToken: TestGroup | TestDesignToken | undefined;
 
     beforeEach(() => {
       parsedGroupOrToken = parseData(testTokenData, parserConfig);
     });
 
     it("returns a design token", () => {
-      expect(parsedGroupOrToken.type).toBe("token");
+      expect(parsedGroupOrToken?.type).toBe("token");
     });
 
     it("does not call parseGroupData function", () => {
@@ -320,32 +325,24 @@ describe("parseData()", () => {
     });
   });
 
-  describe("using addChild functions", () => {
+  describe("using addChildToGroup function", () => {
     const testData = {
       tokenA: { value: 1 },
       tokenB: { value: 2 },
       groupC: { tokenX: { value: 99 }, tokenY: { value: 100 } },
     };
-    const mockAddChild = vi.fn<AddChildFn<TestGroup, TestDesignToken>>(
-      (name, _child) => {
-        parseDataCalls.push({
-          type: "addChild",
-          name,
-        });
-      }
-    );
-    const testContext: TestParentContext = { addChild: mockAddChild };
 
     beforeEach(() => {
-      mockAddChild.mockClear();
-      parseData(testData, parserConfig, testContext);
+      mockAddChildToGroup.mockClear();
+      parserConfig.addChildToGroup = mockAddChildToGroup;
+      parseData(testData, parserConfig);
     });
 
-    it("calls addChild for every child of every group", () => {
+    it("calls addChildToGroup for every child of every group", () => {
       // Root group contains 3 children: "tokenA", "tokenB" and "groupC"
       // "groupC" contains 2 children: "tokenX" and "tokenY"
       // 3 + 2 = 5
-      expect(mockAddChild).toHaveBeenCalledTimes(5);
+      expect(mockAddChildToGroup).toHaveBeenCalledTimes(5);
     });
 
     it("adds a nested group to its parent before parsing its children", () => {
diff --git a/packages/parser-utils/src/parseData.ts b/packages/parser-utils/src/parseData.ts
index 9f240d9..a2b2b46 100644
--- a/packages/parser-utils/src/parseData.ts
+++ b/packages/parser-utils/src/parseData.ts
@@ -39,12 +39,14 @@ export type ParseDesignTokenDataFn<ParsedDesignToken, T> = (
 
 /**
  * A function that adds a parsed group or design token
- * as a child of a parsed group.
+ * as a child of the given parsed group.
  *
+ * @param parent The parent group to add a child to
  * @param name  The name of the child group or design token
- * @param child The group or desing token to add
+ * @param child The group or design token to add
  */
 export type AddChildFn<ParsedGroup, ParsedDesignToken> = (
+  parent: ParsedGroup,
   name: string,
   child: ParsedGroup | ParsedDesignToken
 ) => void;
@@ -52,25 +54,15 @@ export type AddChildFn<ParsedGroup, ParsedDesignToken> = (
 /**
  * The return value of a `ParseGroupDataFn`.
  */
-export interface ParseGroupResult<ParsedGroup, ParsedDesignToken, T> {
+export interface ParseGroupResult<ParsedGroup, T> {
   /**
    * The parsed representation of the group.
    *
-   * May be `undefined` if there is no useful result
-   * to return from `parseData()` - e.g. if just
-   * logging group info or something like that.
+   * May be omitted if there is no useful result to
+   * return and we only need to pass along context
+   * data.
    */
-  group: ParsedGroup;
-
-  /**
-   * Optional function that will add other parsed groups
-   * or design tokens as children of this parsed group.
-   *
-   * Intended for cases where the parsed representation
-   * of a group needs to contain its children. If not
-   * needed, this property can be omitted.
-   */
-  addChild?: AddChildFn<ParsedGroup, ParsedDesignToken>;
+  group?: ParsedGroup;
 
   /**
    * Optional context data to be passed into the
@@ -96,15 +88,14 @@ export interface ParseGroupResult<ParsedGroup, ParsedDesignToken, T> {
  *              parsed the group containing this group.
  *
  * @returns The parsed representation of the group and,
- *          optionally, a function to add child groups or
- *          design tokens to it and some context data to
- *          pass down when child data is parsed.
+ *          optionally, some context data to pass down
+ *          when child data is parsed.
  */
-export type ParseGroupDataFn<ParsedGroup, ParsedDesignToken, T> = (
+export type ParseGroupDataFn<ParsedGroup, T> = (
   data: PlainObject,
   path: string[],
   contextFromParent?: T
-) => ParseGroupResult<ParsedGroup, ParsedDesignToken, T>;
+) => ParseGroupResult<ParsedGroup, T>;
 
 export interface ParserConfig<ParsedDesignToken, ParsedGroup, T> {
   /**
@@ -132,7 +123,7 @@ export interface ParserConfig<ParsedDesignToken, ParsedGroup, T> {
    * path, and should parse that data into whatever structure
    * is desired.
    */
-  parseGroupData: ParseGroupDataFn<ParsedGroup, ParsedDesignToken, T>;
+  parseGroupData?: ParseGroupDataFn<ParsedGroup, T>;
 
   /**
    * Function which is called for each design token
@@ -143,6 +134,16 @@ export interface ParserConfig<ParsedDesignToken, ParsedGroup, T> {
    * desired.
    */
   parseDesignTokenData: ParseDesignTokenDataFn<ParsedDesignToken, T>;
+
+  /**
+   * Optional function that will add parsed groups
+   * or design tokens as children of another parsed group.
+   *
+   * Intended for cases where the parsed representation
+   * of a group needs to contain its children. If not
+   * needed, this property can be omitted.
+   */
+  addChildToGroup?: AddChildFn<ParsedGroup, ParsedDesignToken>;
 }
 
 /**
@@ -192,8 +193,8 @@ function parseDataImpl<ParsedDesignToken, ParsedGroup, T>(
   config: ParserConfig<ParsedDesignToken, ParsedGroup, T>,
   contextFromParent?: T,
   path: string[] = [],
-  addToParent?: AddChildFn<ParsedGroup, ParsedDesignToken>
-): ParsedDesignToken | ParsedGroup {
+  parentGroup?: ParsedGroup
+): ParsedDesignToken | ParsedGroup | undefined {
   if (!isPlainObject(data)) {
     throw new InvalidDataError(path, data);
   }
@@ -203,38 +204,46 @@ function parseDataImpl<ParsedDesignToken, ParsedGroup, T>(
     groupPropsToExtract,
     parseGroupData,
     parseDesignTokenData,
+    addChildToGroup,
   } = config;
 
-  let groupOrToken: ParsedGroup | ParsedDesignToken;
+  let groupOrToken: ParsedGroup | ParsedDesignToken | undefined = undefined;
   if (isDesignTokenData(data)) {
     // looks like a token
     groupOrToken = parseDesignTokenData(data, path, contextFromParent);
-    if (addToParent && path.length > 0) {
-      addToParent(path[path.length - 1], groupOrToken);
+    if (addChildToGroup && path.length > 0 && parentGroup !== undefined) {
+      addChildToGroup(parentGroup, path[path.length - 1], groupOrToken);
     }
   } else {
     // must be a group
-    const { extracted: groupData, remainingProps: childNames } =
-      extractProperties(data, groupPropsToExtract);
-    const { group, addChild, contextForChildren } = parseGroupData(
-      groupData,
-      path,
-      contextFromParent
+    const { extracted: groupData, rest: children } = extractProperties(
+      data,
+      groupPropsToExtract
     );
 
-    groupOrToken = group;
+    let contextForChildren: T | undefined;
+    if (parseGroupData) {
+      const parseResult = parseGroupData(groupData, path, contextFromParent);
+      contextForChildren = parseResult.contextForChildren;
+      groupOrToken = parseResult.group;
+    }
 
-    if (addToParent && path.length > 0) {
-      addToParent(path[path.length - 1], groupOrToken);
+    if (
+      addChildToGroup &&
+      path.length > 0 &&
+      parentGroup !== undefined &&
+      groupOrToken !== undefined
+    ) {
+      addChildToGroup(parentGroup, path[path.length - 1], groupOrToken);
     }
 
-    for (const childName of childNames) {
+    for (const childName in children) {
       parseDataImpl(
-        data[childName],
+        children[childName],
         config,
         contextForChildren,
         [...path, childName],
-        addChild
+        groupOrToken
       );
     }
   }
@@ -266,6 +275,6 @@ export function parseData<ParsedDesignToken, ParsedGroup, T>(
   data: unknown,
   config: ParserConfig<ParsedDesignToken, ParsedGroup, T>,
   contextFromParent?: T
-): ParsedDesignToken | ParsedGroup {
+): ParsedDesignToken | ParsedGroup | undefined {
   return parseDataImpl(data, config, contextFromParent);
 }