diff --git a/frontend/app_flowy/packages/appflowy_editor/lib/appflowy_editor.dart b/frontend/app_flowy/packages/appflowy_editor/lib/appflowy_editor.dart
index e9d22990e5..61dbcc87e6 100644
--- a/frontend/app_flowy/packages/appflowy_editor/lib/appflowy_editor.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/lib/appflowy_editor.dart
@@ -9,7 +9,7 @@ export 'src/document/position.dart';
 export 'src/document/selection.dart';
 export 'src/document/state_tree.dart';
 export 'src/document/text_delta.dart';
-export 'src/document/attributes.dart';
+export 'src/core/document/attributes.dart';
 export 'src/document/built_in_attribute_keys.dart';
 export 'src/editor_state.dart';
 export 'src/operation/operation.dart';
diff --git a/frontend/app_flowy/packages/appflowy_editor/lib/src/commands/format_built_in_text.dart b/frontend/app_flowy/packages/appflowy_editor/lib/src/commands/format_built_in_text.dart
index 758941b198..3a558d0ba6 100644
--- a/frontend/app_flowy/packages/appflowy_editor/lib/src/commands/format_built_in_text.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/lib/src/commands/format_built_in_text.dart
@@ -1,6 +1,6 @@
 import 'package:appflowy_editor/src/commands/format_text.dart';
 import 'package:appflowy_editor/src/commands/text_command_infra.dart';
-import 'package:appflowy_editor/src/document/attributes.dart';
+import 'package:appflowy_editor/src/core/document/attributes.dart';
 import 'package:appflowy_editor/src/document/built_in_attribute_keys.dart';
 import 'package:appflowy_editor/src/core/document/node.dart';
 import 'package:appflowy_editor/src/document/path.dart';
diff --git a/frontend/app_flowy/packages/appflowy_editor/lib/src/commands/format_text.dart b/frontend/app_flowy/packages/appflowy_editor/lib/src/commands/format_text.dart
index 4ed0f80ce1..dbe02aa8c1 100644
--- a/frontend/app_flowy/packages/appflowy_editor/lib/src/commands/format_text.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/lib/src/commands/format_text.dart
@@ -1,7 +1,7 @@
 import 'dart:async';
 
 import 'package:appflowy_editor/src/commands/text_command_infra.dart';
-import 'package:appflowy_editor/src/document/attributes.dart';
+import 'package:appflowy_editor/src/core/document/attributes.dart';
 import 'package:appflowy_editor/src/core/document/node.dart';
 import 'package:appflowy_editor/src/document/path.dart';
 import 'package:appflowy_editor/src/document/selection.dart';
diff --git a/frontend/app_flowy/packages/appflowy_editor/lib/src/document/attributes.dart b/frontend/app_flowy/packages/appflowy_editor/lib/src/core/document/attributes.dart
similarity index 53%
rename from frontend/app_flowy/packages/appflowy_editor/lib/src/document/attributes.dart
rename to frontend/app_flowy/packages/appflowy_editor/lib/src/core/document/attributes.dart
index ff1e258dfc..163e8e9ab6 100644
--- a/frontend/app_flowy/packages/appflowy_editor/lib/src/document/attributes.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/lib/src/core/document/attributes.dart
@@ -23,21 +23,27 @@ Attributes? composeAttributes(
   return attributes.isNotEmpty ? attributes : null;
 }
 
-Attributes invertAttributes(Attributes? base, Attributes? other) {
-  base ??= {};
-  other ??= {};
-  final Attributes attributes = base.keys.fold({}, (previousValue, key) {
-    if (other!.containsKey(key) && other[key] != base![key]) {
-      previousValue[key] = base[key];
+Attributes invertAttributes(Attributes? from, Attributes? to) {
+  from ??= {};
+  to ??= {};
+  final attributes = Attributes.from({});
+
+  // key in from but not in to, or value is different
+  for (final entry in from.entries) {
+    if ((!to.containsKey(entry.key) && entry.value != null) ||
+        to[entry.key] != entry.value) {
+      attributes[entry.key] = entry.value;
     }
-    return previousValue;
-  });
-  return other.keys.fold(attributes, (previousValue, key) {
-    if (!base!.containsKey(key) && other![key] != base[key]) {
-      previousValue[key] = null;
+  }
+
+  // key in to but not in from, or value is different
+  for (final entry in to.entries) {
+    if (!from.containsKey(entry.key) && entry.value != null) {
+      attributes[entry.key] = null;
     }
-    return previousValue;
-  });
+  }
+
+  return attributes;
 }
 
 int hashAttributes(Attributes base) => Object.hashAllUnordered(
diff --git a/frontend/app_flowy/packages/appflowy_editor/lib/src/core/document/node.dart b/frontend/app_flowy/packages/appflowy_editor/lib/src/core/document/node.dart
index 50087194f4..8ed6570f77 100644
--- a/frontend/app_flowy/packages/appflowy_editor/lib/src/core/document/node.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/lib/src/core/document/node.dart
@@ -2,7 +2,7 @@ import 'dart:collection';
 
 import 'package:flutter/material.dart';
 
-import 'package:appflowy_editor/src/document/attributes.dart';
+import 'package:appflowy_editor/src/core/document/attributes.dart';
 import 'package:appflowy_editor/src/document/built_in_attribute_keys.dart';
 import 'package:appflowy_editor/src/document/path.dart';
 import 'package:appflowy_editor/src/document/text_delta.dart';
diff --git a/frontend/app_flowy/packages/appflowy_editor/lib/src/document/state_tree.dart b/frontend/app_flowy/packages/appflowy_editor/lib/src/document/state_tree.dart
index 73e0b5f61f..6b1b5fec7d 100644
--- a/frontend/app_flowy/packages/appflowy_editor/lib/src/document/state_tree.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/lib/src/document/state_tree.dart
@@ -3,7 +3,7 @@ import 'dart:math';
 import 'package:appflowy_editor/src/core/document/node.dart';
 import 'package:appflowy_editor/src/document/path.dart';
 import 'package:appflowy_editor/src/document/text_delta.dart';
-import './attributes.dart';
+import '../core/document/attributes.dart';
 
 class StateTree {
   final Node root;
diff --git a/frontend/app_flowy/packages/appflowy_editor/lib/src/document/text_delta.dart b/frontend/app_flowy/packages/appflowy_editor/lib/src/document/text_delta.dart
index 0d9bc7f2ef..d509a1ef14 100644
--- a/frontend/app_flowy/packages/appflowy_editor/lib/src/document/text_delta.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/lib/src/document/text_delta.dart
@@ -1,7 +1,7 @@
 import 'dart:collection';
 import 'dart:math';
 
-import 'package:appflowy_editor/src/document/attributes.dart';
+import 'package:appflowy_editor/src/core/document/attributes.dart';
 import 'package:flutter/foundation.dart';
 
 // constant number: 2^53 - 1
diff --git a/frontend/app_flowy/packages/appflowy_editor/lib/src/extensions/attributes_extension.dart b/frontend/app_flowy/packages/appflowy_editor/lib/src/extensions/attributes_extension.dart
index b8970d8225..403a007d7f 100644
--- a/frontend/app_flowy/packages/appflowy_editor/lib/src/extensions/attributes_extension.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/lib/src/extensions/attributes_extension.dart
@@ -1,4 +1,4 @@
-import 'package:appflowy_editor/src/document/attributes.dart';
+import 'package:appflowy_editor/src/core/document/attributes.dart';
 import 'package:appflowy_editor/src/document/built_in_attribute_keys.dart';
 import 'package:flutter/material.dart';
 
diff --git a/frontend/app_flowy/packages/appflowy_editor/lib/src/infra/html_converter.dart b/frontend/app_flowy/packages/appflowy_editor/lib/src/infra/html_converter.dart
index e941e023f1..70f3884e4e 100644
--- a/frontend/app_flowy/packages/appflowy_editor/lib/src/infra/html_converter.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/lib/src/infra/html_converter.dart
@@ -1,7 +1,7 @@
 import 'dart:collection';
 import 'dart:ui';
 
-import 'package:appflowy_editor/src/document/attributes.dart';
+import 'package:appflowy_editor/src/core/document/attributes.dart';
 import 'package:appflowy_editor/src/core/document/node.dart';
 import 'package:appflowy_editor/src/document/text_delta.dart';
 import 'package:appflowy_editor/src/extensions/color_extension.dart';
diff --git a/frontend/app_flowy/packages/appflowy_editor/lib/src/operation/transaction_builder.dart b/frontend/app_flowy/packages/appflowy_editor/lib/src/operation/transaction_builder.dart
index 7b606a8441..64127701b4 100644
--- a/frontend/app_flowy/packages/appflowy_editor/lib/src/operation/transaction_builder.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/lib/src/operation/transaction_builder.dart
@@ -1,7 +1,7 @@
 import 'dart:collection';
 import 'dart:math';
 
-import 'package:appflowy_editor/src/document/attributes.dart';
+import 'package:appflowy_editor/src/core/document/attributes.dart';
 import 'package:appflowy_editor/src/core/document/node.dart';
 import 'package:appflowy_editor/src/document/path.dart';
 import 'package:appflowy_editor/src/document/position.dart';
diff --git a/frontend/app_flowy/packages/appflowy_editor/lib/src/service/default_text_operations/format_rich_text_style.dart b/frontend/app_flowy/packages/appflowy_editor/lib/src/service/default_text_operations/format_rich_text_style.dart
index 620816f165..94e34c5297 100644
--- a/frontend/app_flowy/packages/appflowy_editor/lib/src/service/default_text_operations/format_rich_text_style.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/lib/src/service/default_text_operations/format_rich_text_style.dart
@@ -1,4 +1,4 @@
-import 'package:appflowy_editor/src/document/attributes.dart';
+import 'package:appflowy_editor/src/core/document/attributes.dart';
 import 'package:appflowy_editor/src/core/document/node.dart';
 import 'package:appflowy_editor/src/document/position.dart';
 import 'package:appflowy_editor/src/document/selection.dart';
diff --git a/frontend/app_flowy/packages/appflowy_editor/lib/src/service/internal_key_event_handlers/number_list_helper.dart b/frontend/app_flowy/packages/appflowy_editor/lib/src/service/internal_key_event_handlers/number_list_helper.dart
index ed9018a71e..0c2a3ab9e2 100644
--- a/frontend/app_flowy/packages/appflowy_editor/lib/src/service/internal_key_event_handlers/number_list_helper.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/lib/src/service/internal_key_event_handlers/number_list_helper.dart
@@ -2,7 +2,7 @@ import 'package:appflowy_editor/src/document/selection.dart';
 import 'package:appflowy_editor/src/editor_state.dart';
 import 'package:appflowy_editor/src/document/built_in_attribute_keys.dart';
 import 'package:appflowy_editor/src/operation/transaction_builder.dart';
-import 'package:appflowy_editor/src/document/attributes.dart';
+import 'package:appflowy_editor/src/core/document/attributes.dart';
 
 void makeFollowingNodesIncremental(
     EditorState editorState, List<int> insertPath, Selection afterSelection,
diff --git a/frontend/app_flowy/packages/appflowy_editor/test/core/document/attributes_test.dart b/frontend/app_flowy/packages/appflowy_editor/test/core/document/attributes_test.dart
new file mode 100644
index 0000000000..873ab2788b
--- /dev/null
+++ b/frontend/app_flowy/packages/appflowy_editor/test/core/document/attributes_test.dart
@@ -0,0 +1,59 @@
+import 'package:appflowy_editor/appflowy_editor.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() async {
+  group('attributes.dart', () {
+    test('composeAttributes', () {
+      final base = {
+        'a': 1,
+        'b': 2,
+      };
+      final other = {
+        'b': 3,
+        'c': 4,
+        'd': null,
+      };
+      expect(composeAttributes(base, other, keepNull: false), {
+        'a': 1,
+        'b': 3,
+        'c': 4,
+      });
+      expect(composeAttributes(base, other, keepNull: true), {
+        'a': 1,
+        'b': 3,
+        'c': 4,
+        'd': null,
+      });
+      expect(composeAttributes(null, other, keepNull: false), {
+        'b': 3,
+        'c': 4,
+      });
+      expect(composeAttributes(base, null, keepNull: false), {
+        'a': 1,
+        'b': 2,
+      });
+    });
+
+    test('invertAttributes', () {
+      final base = {
+        'a': 1,
+        'b': 2,
+      };
+      final other = {
+        'b': 3,
+        'c': 4,
+        'd': null,
+      };
+      expect(invertAttributes(base, other), {
+        'a': 1,
+        'b': 2,
+        'c': null,
+      });
+      expect(invertAttributes(other, base), {
+        'a': null,
+        'b': 3,
+        'c': 4,
+      });
+    });
+  });
+}
diff --git a/frontend/app_flowy/packages/appflowy_editor/test/document/node_test.dart b/frontend/app_flowy/packages/appflowy_editor/test/core/document/node_test.dart
similarity index 70%
rename from frontend/app_flowy/packages/appflowy_editor/test/document/node_test.dart
rename to frontend/app_flowy/packages/appflowy_editor/test/core/document/node_test.dart
index cf03d98cdf..aa78bf7a7c 100644
--- a/frontend/app_flowy/packages/appflowy_editor/test/document/node_test.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/test/core/document/node_test.dart
@@ -147,5 +147,68 @@ void main() async {
       expect(identical(node.children, base.children), false);
       expect(identical(node.children.first, base.children.first), false);
     });
+
+    test('test insert', () {
+      final base = Node(
+        type: 'base',
+      );
+
+      // insert at the front
+      final childA = Node(
+        type: 'child',
+      );
+      base.insert(childA, index: -1);
+      expect(
+        identical(base.childAtIndex(0), childA),
+        true,
+      );
+
+      // insert at the last
+      final childB = Node(
+        type: 'child',
+      );
+      base.insert(childB, index: 1000);
+      expect(
+        identical(base.childAtIndex(base.children.length - 1), childB),
+        true,
+      );
+
+      // insert at the last
+      final childC = Node(
+        type: 'child',
+      );
+      base.insert(childC);
+      expect(
+        identical(base.childAtIndex(base.children.length - 1), childC),
+        true,
+      );
+    });
+
+    test('test fromJson', () {
+      final node = Node.fromJson({
+        'type': 'example',
+        'attributes': {
+          'example': 'example',
+        },
+        'children': [
+          {
+            'type': 'example',
+            'attributes': {
+              'example': 'example',
+            },
+          },
+        ],
+      });
+      expect(node.type, 'example');
+      expect(node.attributes, {'example': 'example'});
+      expect(node.children.length, 1);
+      expect(node.children.first.type, 'example');
+      expect(node.children.first.attributes, {'example': 'example'});
+    });
+
+    test('test toPlainText', () {
+      final textNode = TextNode.empty()..delta = (Delta()..insert('AppFlowy'));
+      expect(textNode.toPlainText(), 'AppFlowy');
+    });
   });
 }
diff --git a/frontend/app_flowy/packages/appflowy_editor/test/legacy/delta_test.dart b/frontend/app_flowy/packages/appflowy_editor/test/legacy/delta_test.dart
index 4593c757d3..3c8d4a3dfe 100644
--- a/frontend/app_flowy/packages/appflowy_editor/test/legacy/delta_test.dart
+++ b/frontend/app_flowy/packages/appflowy_editor/test/legacy/delta_test.dart
@@ -1,4 +1,4 @@
-import 'package:appflowy_editor/src/document/attributes.dart';
+import 'package:appflowy_editor/src/core/document/attributes.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:appflowy_editor/src/document/text_delta.dart';