diff --git a/lib/kdbx.dart b/lib/kdbx.dart
index be1dc2f..f0c3bed 100644
--- a/lib/kdbx.dart
+++ b/lib/kdbx.dart
@@ -9,10 +9,19 @@ export 'src/kdbx_binary.dart' show KdbxBinary;
 export 'src/kdbx_consts.dart';
 export 'src/kdbx_custom_data.dart';
 export 'src/kdbx_dao.dart' show KdbxDao;
-export 'src/kdbx_entry.dart';
+export 'src/kdbx_entry.dart' show KdbxEntry, KdbxKey;
 export 'src/kdbx_file.dart';
-export 'src/kdbx_format.dart';
-export 'src/kdbx_group.dart';
+export 'src/kdbx_format.dart'
+    show
+        KdbxBody,
+        Credentials,
+        CredentialsPart,
+        HashCredentials,
+        KdbxFormat,
+        KeyFileComposite,
+        KeyFileCredentials,
+        PasswordCredentials;
+export 'src/kdbx_group.dart' show KdbxGroup;
 export 'src/kdbx_header.dart'
     show
         KdbxException,
@@ -21,5 +30,12 @@ export 'src/kdbx_header.dart'
         KdbxUnsupportedException,
         KdbxVersion;
 export 'src/kdbx_meta.dart';
-export 'src/kdbx_object.dart';
+export 'src/kdbx_object.dart'
+    show
+        KdbxUuid,
+        KdbxObject,
+        KdbxNode,
+        Changeable,
+        ChangeEvent,
+        KdbxNodeContext;
 export 'src/utils/byte_utils.dart' show ByteUtils;
diff --git a/lib/src/kdbx_binary.dart b/lib/src/kdbx_binary.dart
index d1f3065..ff68866 100644
--- a/lib/src/kdbx_binary.dart
+++ b/lib/src/kdbx_binary.dart
@@ -6,6 +6,7 @@ import 'package:kdbx/src/utils/byte_utils.dart';
 import 'package:kdbx/src/kdbx_header.dart';
 import 'package:kdbx/src/kdbx_xml.dart';
 import 'package:meta/meta.dart';
+import 'package:quiver/core.dart';
 import 'package:xml/xml.dart';
 
 class KdbxBinary {
@@ -13,6 +14,7 @@ class KdbxBinary {
   final bool isInline;
   final bool isProtected;
   final Uint8List value;
+  int _valueHashCode;
 
   static KdbxBinary readBinaryInnerHeader(InnerHeaderField field) {
     final flags = field.bytes[0];
@@ -25,6 +27,11 @@ class KdbxBinary {
     );
   }
 
+  int get valueHashCode => _valueHashCode ??= hashObjects(value);
+
+  bool valueEqual(KdbxBinary other) =>
+      valueHashCode == other.valueHashCode && ByteUtils.eq(value, value);
+
   InnerHeaderField writeToInnerHeader() {
     final writer = WriterHelper();
     final flags = isProtected ? 0x01 : 0x00;
diff --git a/lib/src/kdbx_custom_data.dart b/lib/src/kdbx_custom_data.dart
index ae6426e..77b2f74 100644
--- a/lib/src/kdbx_custom_data.dart
+++ b/lib/src/kdbx_custom_data.dart
@@ -28,6 +28,8 @@ class KdbxCustomData extends KdbxNode {
     modify(() => _data[key] = value);
   }
 
+  bool containsKey(String key) => _data.containsKey(key);
+
   @override
   xml.XmlElement toXml() {
     final el = super.toXml();
diff --git a/lib/src/kdbx_dao.dart b/lib/src/kdbx_dao.dart
index 69b8e4b..a3cc190 100644
--- a/lib/src/kdbx_dao.dart
+++ b/lib/src/kdbx_dao.dart
@@ -1,5 +1,7 @@
-import 'package:kdbx/kdbx.dart';
+import 'package:kdbx/src/kdbx_entry.dart';
 import 'package:kdbx/src/kdbx_file.dart';
+import 'package:kdbx/src/kdbx_group.dart';
+import 'package:kdbx/src/kdbx_object.dart';
 import 'package:meta/meta.dart';
 
 /// Helper object for accessing and modifing data inside
diff --git a/lib/src/kdbx_deleted_object.dart b/lib/src/kdbx_deleted_object.dart
index 4f95c9d..b88ed98 100644
--- a/lib/src/kdbx_deleted_object.dart
+++ b/lib/src/kdbx_deleted_object.dart
@@ -1,4 +1,5 @@
-import 'package:kdbx/kdbx.dart';
+import 'package:kdbx/src/kdbx_format.dart';
+import 'package:kdbx/src/kdbx_object.dart';
 import 'package:kdbx/src/kdbx_xml.dart';
 import 'package:xml/xml.dart';
 
diff --git a/lib/src/kdbx_entry.dart b/lib/src/kdbx_entry.dart
index 18df046..edd5628 100644
--- a/lib/src/kdbx_entry.dart
+++ b/lib/src/kdbx_entry.dart
@@ -1,11 +1,11 @@
 import 'dart:typed_data';
 
-import 'package:kdbx/kdbx.dart';
 import 'package:kdbx/src/crypto/protected_value.dart';
 import 'package:kdbx/src/internal/extension_utils.dart';
 import 'package:kdbx/src/kdbx_binary.dart';
 import 'package:kdbx/src/kdbx_consts.dart';
 import 'package:kdbx/src/kdbx_file.dart';
+import 'package:kdbx/src/kdbx_format.dart';
 import 'package:kdbx/src/kdbx_group.dart';
 import 'package:kdbx/src/kdbx_header.dart';
 import 'package:kdbx/src/kdbx_object.dart';
@@ -13,6 +13,7 @@ import 'package:kdbx/src/kdbx_xml.dart';
 import 'package:logging/logging.dart';
 import 'package:meta/meta.dart';
 import 'package:path/path.dart' as path;
+import 'package:quiver/check.dart';
 import 'package:xml/xml.dart';
 
 final _logger = Logger('kdbx.kdbx_entry');
@@ -37,10 +38,74 @@ class KdbxKey {
   }
 }
 
+extension KdbxEntryInternal on KdbxEntry {
+  KdbxEntry cloneInto(KdbxGroup otherGroup, {bool toHistoryEntry = false}) =>
+      KdbxEntry.create(
+        otherGroup.file,
+        otherGroup,
+        isHistoryEntry: toHistoryEntry,
+      )
+        ..forceSetUuid(uuid)
+        ..let(toHistoryEntry ? (x) => null : otherGroup.addEntry)
+        .._overwriteFrom(
+          OverwriteContext.noop,
+          this,
+          includeHistory: !toHistoryEntry,
+        );
+
+  List<KdbxSubNode> get _overwriteNodes => [
+        ...objectNodes,
+        foregroundColor,
+        backgroundColor,
+        overrideURL,
+        tags,
+      ];
+
+  void _overwriteFrom(
+    OverwriteContext overwriteContext,
+    KdbxEntry other, {
+    bool includeHistory = false,
+  }) {
+    // we only support overwriting history, if it is empty.
+    checkArgument(!includeHistory || history.isEmpty,
+        message:
+            'We can only overwrite with history, if local history is empty.');
+    assertSameUuid(other, 'overwrite');
+    overwriteSubNodesFrom(
+      overwriteContext,
+      _overwriteNodes,
+      other._overwriteNodes,
+    );
+    // overwrite all strings
+    _strings.clear();
+    _strings.addAll(other._strings);
+    // overwrite all binaries
+    final newBinaries = other._binaries.map((key, value) => MapEntry(
+          key,
+          ctx.findBinaryByValue(value) ??
+              (value..let((that) => ctx.addBinary(that))),
+        ));
+    _binaries.clear();
+    _binaries.addAll(newBinaries);
+    times.overwriteFrom(other.times);
+    if (includeHistory) {
+      for (final historyEntry in other.history) {
+        history.add(historyEntry.cloneInto(parent, toHistoryEntry: false));
+      }
+    }
+  }
+}
+
 class KdbxEntry extends KdbxObject {
-  KdbxEntry.create(KdbxFile file, KdbxGroup parent)
-      : isHistoryEntry = false,
-        history = [],
+  /// Creates a new entry in the given parent group.
+  /// callers are still responsible for calling [parent.addEntry(..)]!
+  ///
+  /// FIXME: this makes no sense, we should automatically attach this to the parent.
+  KdbxEntry.create(
+    KdbxFile file,
+    KdbxGroup parent, {
+    this.isHistoryEntry = false,
+  })  : history = [],
         super.create(file.ctx, file, 'Entry', parent) {
     icon.set(KdbxIcon.Key);
   }
@@ -89,6 +154,11 @@ class KdbxEntry extends KdbxObject {
 
   final List<KdbxEntry> history;
 
+  ColorNode get foregroundColor => ColorNode(this, 'ForegroundColor');
+  ColorNode get backgroundColor => ColorNode(this, 'BackgroundColor');
+  StringNode get overrideURL => StringNode(this, 'OverrideURL');
+  StringNode get tags => StringNode(this, 'Tags');
+
   @override
   set file(KdbxFile file) {
     super.file = file;
@@ -102,7 +172,12 @@ class KdbxEntry extends KdbxObject {
   @override
   void onBeforeModify() {
     super.onBeforeModify();
-    history.add(KdbxEntry.read(ctx, parent, toXml())..file = file);
+    history.add(KdbxEntry.read(
+      ctx,
+      parent,
+      toXml(),
+      isHistoryEntry: true,
+    )..file = file);
   }
 
   @override
@@ -251,6 +326,45 @@ class KdbxEntry extends KdbxObject {
     throw StateError('Unable to find unique name for $fileName');
   }
 
+  static KdbxEntry _findHistoryEntry(
+          List<KdbxEntry> history, DateTime lastModificationTime) =>
+      history.firstWhere(
+          (history) =>
+              history.times.lastModificationTime.get() == lastModificationTime,
+          orElse: () => null);
+
+  @override
+  void merge(MergeContext mergeContext, KdbxEntry other) {
+    assertSameUuid(other, 'merge');
+    if (other.wasModifiedAfter(this)) {
+      // other object is newer, create new history entry and copy fields.
+      modify(() => _overwriteFrom(mergeContext, other));
+    } else if (wasModifiedAfter(other)) {
+      // we are newer. check if the old revision lives on in our history.
+      final ourLastModificationTime = times.lastModificationTime.get();
+      final historyEntry = _findHistoryEntry(history, ourLastModificationTime);
+      if (historyEntry == null) {
+        // it seems like we don't know about that state, so we have to add
+        // it to history.
+        history.add(other.cloneInto(parent, toHistoryEntry: true));
+      }
+    }
+    // copy missing history entries.
+    for (final otherHistoryEntry in other.history) {
+      final meHistoryEntry = _findHistoryEntry(
+          history, otherHistoryEntry.times.lastModificationTime.get());
+      if (meHistoryEntry == null) {
+        mergeContext.trackChange(
+          this,
+          debug: 'merge in history '
+              '${otherHistoryEntry.times.lastModificationTime.get()}',
+        );
+        history.add(otherHistoryEntry.cloneInto(parent, toHistoryEntry: true));
+      }
+    }
+    mergeContext.markAsMerged(this);
+  }
+
   @override
   String toString() {
     return 'KdbxGroup{uuid=$uuid,name=$label}';
diff --git a/lib/src/kdbx_file.dart b/lib/src/kdbx_file.dart
index 01c2520..3477872 100644
--- a/lib/src/kdbx_file.dart
+++ b/lib/src/kdbx_file.dart
@@ -119,6 +119,17 @@ class KdbxFile {
     body.meta.headerHash.remove();
     header.upgrade(majorVersion);
   }
+
+  /// Merges the given file into this file.
+  /// Both files must have the same origin (ie. same root group UUID).
+  /// FIXME: THiS iS NOT YET FINISHED, DO NOT USE.
+  void merge(KdbxFile other) {
+    if (other.body.rootGroup.uuid != body.rootGroup.uuid) {
+      throw KdbxUnsupportedException(
+          'Root groups of source and dest file do not match.');
+    }
+    body.merge(other.body);
+  }
 }
 
 class CachedValue<T> {
diff --git a/lib/src/kdbx_format.dart b/lib/src/kdbx_format.dart
index 0e64114..96bff0b 100644
--- a/lib/src/kdbx_format.dart
+++ b/lib/src/kdbx_format.dart
@@ -4,6 +4,7 @@ import 'dart:io';
 import 'dart:typed_data';
 
 import 'package:archive/archive.dart';
+import 'package:supercharged_dart/supercharged_dart.dart';
 import 'package:argon2_ffi_base/argon2_ffi_base.dart';
 import 'package:convert/convert.dart' as convert;
 import 'package:crypto/crypto.dart' as crypto;
@@ -27,6 +28,7 @@ import 'package:kdbx/src/kdbx_xml.dart';
 import 'package:logging/logging.dart';
 import 'package:meta/meta.dart';
 import 'package:pointycastle/export.dart';
+import 'package:quiver/iterables.dart';
 import 'package:xml/xml.dart' as xml;
 
 final _logger = Logger('kdbx.format');
@@ -72,7 +74,8 @@ class KdbxReadWriteContext {
     @required this.header,
   })  : assert(binaries != null),
         assert(header != null),
-        _binaries = binaries;
+        _binaries = binaries,
+        _deletedObjects = [];
 
   static final kdbxContext = Expando<KdbxReadWriteContext>();
 
@@ -89,8 +92,10 @@ class KdbxReadWriteContext {
     kdbxContext[node.document] = ctx;
   }
 
+  // TODO make [_binaries] and [_deletedObjects] late init :-)
   @protected
   final List<KdbxBinary> _binaries;
+  final List<KdbxDeletedObject> _deletedObjects;
 
   Iterable<KdbxBinary> get binariesIterable => _binaries;
 
@@ -98,6 +103,12 @@ class KdbxReadWriteContext {
 
   int get versionMajor => header.version.major;
 
+  void initContext(Iterable<KdbxBinary> binaries,
+      Iterable<KdbxDeletedObject> deletedObjects) {
+    _binaries.addAll(binaries);
+    _deletedObjects.addAll(deletedObjects);
+  }
+
   KdbxBinary binaryById(int id) {
     if (id >= _binaries.length) {
       return null;
@@ -109,6 +120,12 @@ class KdbxReadWriteContext {
     _binaries.add(binary);
   }
 
+  KdbxBinary findBinaryByValue(KdbxBinary binary) {
+    // TODO create a hashset or map?
+    return _binaries.firstWhere((element) => element.valueEqual(binary),
+        orElse: () => null);
+  }
+
   /// finds the ID of the given binary.
   /// if it can't be found, [KdbxCorruptedFileException] is thrown.
   int findBinaryId(KdbxBinary binary) {
@@ -193,9 +210,7 @@ class HashCredentials implements Credentials {
 }
 
 class KdbxBody extends KdbxNode {
-  KdbxBody.create(this.meta, this.rootGroup)
-      : _deletedObjects = [],
-        super.create('KeePassFile') {
+  KdbxBody.create(this.meta, this.rootGroup) : super.create('KeePassFile') {
     node.children.add(meta.node);
     final rootNode = xml.XmlElement(xml.XmlName('Root'));
     node.children.add(rootNode);
@@ -206,17 +221,14 @@ class KdbxBody extends KdbxNode {
     xml.XmlElement node,
     this.meta,
     this.rootGroup,
-    Iterable<KdbxDeletedObject> deletedObjects,
-  )   : _deletedObjects = List.of(deletedObjects),
-        super.read(node);
+  ) : super.read(node);
 
 //  final xml.XmlDocument xmlDocument;
   final KdbxMeta meta;
   final KdbxGroup rootGroup;
-  final List<KdbxDeletedObject> _deletedObjects;
 
   @visibleForTesting
-  List<KdbxDeletedObject> get deletedObjects => _deletedObjects;
+  List<KdbxDeletedObject> get deletedObjects => ctx._deletedObjects;
 
   Future<void> writeV3(WriterHelper writer, KdbxFile kdbxFile,
       ProtectedSaltGenerator saltGenerator) async {
@@ -284,6 +296,63 @@ class KdbxBody extends KdbxNode {
     }
   }
 
+  KdbxReadWriteContext get ctx => rootGroup.ctx;
+
+  Map<KdbxUuid, KdbxObject> _createObjectIndex() => Map.fromEntries(
+      concat([rootGroup.getAllGroups(), rootGroup.getAllEntries()])
+          .map((e) => MapEntry(e.uuid, e)));
+
+  void merge(KdbxBody other) {
+    // sync deleted objects.
+    final deleted =
+        Map.fromEntries(ctx._deletedObjects.map((e) => MapEntry(e.uuid, e)));
+    final incomingDeleted = <KdbxUuid, KdbxDeletedObject>{};
+
+    for (final obj in other.ctx._deletedObjects) {
+      if (!deleted.containsKey(obj.uuid)) {
+        final del = KdbxDeletedObject.create(ctx, obj.uuid);
+        ctx._deletedObjects.add(del);
+        incomingDeleted[del.uuid] = del;
+        deleted[del.uuid] = del;
+      }
+    }
+
+    final mergeContext = MergeContext(
+      objectIndex: _createObjectIndex(),
+      deletedObjects: deleted,
+    );
+
+    // sync binaries
+    for (final binary in other.ctx.binariesIterable) {
+      if (ctx.findBinaryByValue(binary) == null) {
+        ctx.addBinary(binary);
+        mergeContext.trackChange(this,
+            debug: 'adding new binary ${binary.value.length}');
+      }
+    }
+    meta.merge(other.meta);
+    rootGroup.merge(mergeContext, other.rootGroup);
+
+    // remove deleted objects
+    for (final incomingDelete in incomingDeleted.values) {
+      final object = mergeContext.objectIndex[incomingDelete.uuid];
+      mergeContext.trackChange(object, debug: 'was deleted.');
+    }
+
+    // FIXME do some cleanup.
+
+    _logger.info('Finished merging. ${mergeContext.debugChanges()}');
+    final incomingObjects = other._createObjectIndex();
+    _logger.info('Merged: ${mergeContext.merged} vs. '
+        '(local objects: ${mergeContext.objectIndex.length}, '
+        'incoming objects: ${incomingObjects.length})');
+
+    // sanity checks
+    if (mergeContext.merged.keys.length != mergeContext.objectIndex.length) {
+      // TODO figure out what went wrong.
+    }
+  }
+
   xml.XmlDocument generateXml(ProtectedSaltGenerator saltGenerator) {
     final rootGroupNode = rootGroup.toXml();
     // update protected values...
@@ -316,7 +385,7 @@ class KdbxBody extends KdbxNode {
               rootGroupNode,
               XmlUtils.createNode(
                 KdbxXml.NODE_DELETED_OBJECTS,
-                _deletedObjects.map((e) => e.toXml()).toList(),
+                ctx._deletedObjects.map((e) => e.toXml()).toList(),
               ),
             ]),
       ],
@@ -330,6 +399,65 @@ class KdbxBody extends KdbxNode {
   }
 }
 
+abstract class OverwriteContext {
+  const OverwriteContext();
+  static const noop = OverwriteContextNoop();
+  void trackChange(KdbxObject object, {String node, String debug});
+}
+
+class OverwriteContextNoop implements OverwriteContext {
+  const OverwriteContextNoop();
+  @override
+  void trackChange(KdbxObject object, {String node, String debug}) {}
+}
+
+class MergeChange {
+  MergeChange({this.object, this.node, this.debug});
+
+  final KdbxNode object;
+
+  /// the name of the subnode of [object].
+  final String node;
+  final String debug;
+}
+
+class MergeContext implements OverwriteContext {
+  MergeContext({this.objectIndex, this.deletedObjects});
+  final Map<KdbxUuid, KdbxObject> objectIndex;
+  final Map<KdbxUuid, KdbxDeletedObject> deletedObjects;
+  final Map<KdbxUuid, KdbxObject> merged = {};
+  final List<MergeChange> changes = [];
+
+  void markAsMerged(KdbxObject object) {
+    if (merged.containsKey(object.uuid)) {
+      throw StateError(
+          'object was already market as merged! ${object.uuid}: $object');
+    }
+    merged[object.uuid] = object;
+  }
+
+  @override
+  void trackChange(KdbxNode object, {String node, String debug}) {
+    changes.add(MergeChange(
+      object: object,
+      node: node,
+      debug: debug,
+    ));
+  }
+
+  String debugChanges() {
+    final group =
+        changes.groupBy((element) => element.object, valueTransform: (x) => x);
+    return group.entries
+        .map((e) => [
+              e.key.toString(),
+              ':    ',
+              ...e.value.map((e) => e.toString()),
+            ].join('\n    '))
+        .join('\n');
+  }
+}
+
 class _KeysV4 {
   _KeysV4(this.hmacKey, this.cipherKey);
 
@@ -645,15 +773,12 @@ class KdbxFormat {
     final root = keePassFile.findElements('Root').single;
 
     final kdbxMeta = KdbxMeta.read(meta, ctx);
-    if (kdbxMeta.binaries?.isNotEmpty == true) {
-      ctx._binaries.addAll(kdbxMeta.binaries);
-    } else if (header.innerHeader.binaries.isNotEmpty) {
-      ctx._binaries.addAll(header.innerHeader.binaries
-          .map((e) => KdbxBinary.readBinaryInnerHeader(e)));
-    }
+    // kdbx < 4 has binaries in the meta section, >= 4 in the binary header.
+    final binaries = kdbxMeta.binaries?.isNotEmpty == true
+        ? kdbxMeta.binaries
+        : header.innerHeader.binaries
+            .map((e) => KdbxBinary.readBinaryInnerHeader(e));
 
-    final rootGroup =
-        KdbxGroup.read(ctx, null, root.findElements(KdbxXml.NODE_GROUP).single);
     final deletedObjects = root
             .findElements(KdbxXml.NODE_DELETED_OBJECTS)
             .singleOrNull
@@ -661,8 +786,12 @@ class KdbxFormat {
                 .findElements(KdbxDeletedObject.NODE_NAME)
                 .map((node) => KdbxDeletedObject.read(node, ctx))) ??
         [];
+    ctx.initContext(binaries, deletedObjects);
+
+    final rootGroup =
+        KdbxGroup.read(ctx, null, root.findElements(KdbxXml.NODE_GROUP).single);
     _logger.fine('successfully read Meta.');
-    return KdbxBody.read(keePassFile, kdbxMeta, rootGroup, deletedObjects);
+    return KdbxBody.read(keePassFile, kdbxMeta, rootGroup);
   }
 
   Uint8List _decryptContent(
diff --git a/lib/src/kdbx_group.dart b/lib/src/kdbx_group.dart
index acebe51..2af4ea6 100644
--- a/lib/src/kdbx_group.dart
+++ b/lib/src/kdbx_group.dart
@@ -1,18 +1,22 @@
 import 'package:kdbx/kdbx.dart';
 import 'package:kdbx/src/kdbx_consts.dart';
 import 'package:kdbx/src/kdbx_entry.dart';
+import 'package:kdbx/src/kdbx_format.dart';
 import 'package:kdbx/src/kdbx_xml.dart';
+import 'package:logging/logging.dart';
 import 'package:meta/meta.dart';
 import 'package:xml/xml.dart';
 
 import 'kdbx_object.dart';
 
+final _logger = Logger('kdbx_group');
+
 class KdbxGroup extends KdbxObject {
-  KdbxGroup.create(
-      {@required KdbxReadWriteContext ctx,
-      @required KdbxGroup parent,
-      @required String name})
-      : super.create(
+  KdbxGroup.create({
+    @required KdbxReadWriteContext ctx,
+    @required KdbxGroup parent,
+    @required String name,
+  }) : super.create(
           ctx,
           parent?.file,
           KdbxXml.NODE_GROUP,
@@ -65,6 +69,8 @@ class KdbxGroup extends KdbxObject {
       throw StateError(
           'Invalid operation. Trying to add entry which is already in another group.');
     }
+    assert(_entries.findByUuid(entry.uuid) == null,
+        'must not already be in this group.');
     modify(() => _entries.add(entry));
   }
 
@@ -76,36 +82,127 @@ class KdbxGroup extends KdbxObject {
     modify(() => _groups.add(group));
   }
 
-  void internalRemoveGroup(KdbxGroup group) {
-    modify(() {
-      if (!_groups.remove(group)) {
-        throw StateError('Unable to remove $group from $this (Not found)');
-      }
-    });
-  }
-
-  void internalRemoveEntry(KdbxEntry entry) {
-    modify(() {
-      if (!_entries.remove(entry)) {
-        throw StateError('Unable to remove $entry from $this (Not found)');
-      }
-    });
-  }
-
   /// returns all parents recursively including this group.
   List<KdbxGroup> get breadcrumbs => [...?parent?.breadcrumbs, this];
 
   StringNode get name => StringNode(this, 'Name');
 
+  StringNode get notes => StringNode(this, 'Notes');
+
 //  String get name => text('Name') ?? '';
   BooleanNode get expanded => BooleanNode(this, 'IsExpanded');
 
+  StringNode get defaultAutoTypeSequence =>
+      StringNode(this, 'DefaultAutoTypeSequence');
+
   BooleanNode get enableAutoType => BooleanNode(this, 'EnableAutoType');
 
   BooleanNode get enableSearching => BooleanNode(this, 'EnableSearching');
 
+  UuidNode get lastTopVisibleEntry => UuidNode(this, 'LastTopVisibleEntry');
+
+  @override
+  void merge(MergeContext mergeContext, KdbxGroup other) {
+    assertSameUuid(other, 'merge');
+
+    if (other.wasModifiedAfter(this)) {
+      _logger.finest('merge: other group was modified $uuid');
+      _overwriteFrom(mergeContext, other);
+    }
+    _mergeSubObjects<KdbxGroup>(
+      mergeContext,
+      _groups,
+      other._groups,
+      importToHere: (other) =>
+          KdbxGroup.create(ctx: ctx, parent: this, name: other.name.get())
+            ..forceSetUuid(other.uuid)
+            .._overwriteFrom(mergeContext, other),
+    );
+    _mergeSubObjects<KdbxEntry>(
+      mergeContext,
+      _entries,
+      other._entries,
+      importToHere: (other) => other.cloneInto(this),
+    );
+  }
+
+  void _mergeSubObjects<T extends KdbxObject>(
+      MergeContext mergeContext, List<T> me, List<T> other,
+      {@required T Function(T obj) importToHere}) {
+    // possibilities:
+    // 1. Not changed at all 👍
+    // 2. Deleted in other
+    // 3. Deleted in this
+    // 4. Modified in other
+    // 5. Modified in this
+    // 6. Moved in other
+    // 7. Moved in this
+
+    for (final otherObj in other) {
+      final meObj = me.findByUuid(otherObj.uuid);
+      if (meObj == null) {
+        // moved or deleted.
+
+        final movedObj = mergeContext.objectIndex[otherObj.uuid];
+        if (movedObj == null) {
+          // item was created in the other file. we have to import it
+          importToHere(otherObj);
+        } else {
+          // item was moved.
+          if (otherObj.wasMovedAfter(movedObj)) {
+            // item was moved in the other file, so we have to move it here.
+            file.move(movedObj, this);
+          } else {
+            // item was moved in this file, so nothing to do.
+          }
+          movedObj.merge(mergeContext, otherObj);
+        }
+      } else {
+        meObj.merge(mergeContext, otherObj);
+      }
+    }
+    mergeContext.markAsMerged(this);
+  }
+
+  List<KdbxSubNode> get _overwriteNodes => [
+        ...objectNodes,
+        name,
+        notes,
+        expanded,
+        defaultAutoTypeSequence,
+        enableAutoType,
+        enableSearching,
+        lastTopVisibleEntry,
+      ];
+
+  void _overwriteFrom(MergeContext mergeContext, KdbxGroup other) {
+    assertSameUuid(other, 'overwrite');
+    overwriteSubNodesFrom(mergeContext, _overwriteNodes, other._overwriteNodes);
+    // we should probably check that [lastTopVisibleEntry] is still a
+    // valid reference?
+    times.overwriteFrom(other.times);
+  }
+
   @override
   String toString() {
     return 'KdbxGroup{uuid=$uuid,name=${name.get()}}';
   }
 }
+
+extension KdbxGroupInternal on KdbxGroup {
+  void internalRemoveGroup(KdbxGroup group) {
+    modify(() {
+      if (!_groups.remove(group)) {
+        throw StateError('Unable to remove $group from $this (Not found)');
+      }
+    });
+  }
+
+  void internalRemoveEntry(KdbxEntry entry) {
+    modify(() {
+      if (!_entries.remove(entry)) {
+        throw StateError('Unable to remove $entry from $this (Not found)');
+      }
+    });
+  }
+}
diff --git a/lib/src/kdbx_meta.dart b/lib/src/kdbx_meta.dart
index 58c1977..8439c80 100644
--- a/lib/src/kdbx_meta.dart
+++ b/lib/src/kdbx_meta.dart
@@ -2,10 +2,10 @@ import 'dart:convert';
 import 'dart:typed_data';
 
 import 'package:collection/collection.dart';
-import 'package:kdbx/kdbx.dart';
 import 'package:kdbx/src/internal/extension_utils.dart';
 import 'package:kdbx/src/kdbx_binary.dart';
 import 'package:kdbx/src/kdbx_custom_data.dart';
+import 'package:kdbx/src/kdbx_format.dart';
 import 'package:kdbx/src/kdbx_header.dart';
 import 'package:kdbx/src/kdbx_object.dart';
 import 'package:kdbx/src/kdbx_xml.dart';
@@ -165,6 +165,46 @@ class KdbxMeta extends KdbxNode implements KdbxNodeContext {
     );
     return ret;
   }
+
+  // Merge in changes in [other] into this meta data.
+  void merge(KdbxMeta other) {
+    // FIXME make sure this is finished
+    if (other.databaseNameChanged.isAfter(databaseNameChanged)) {
+      databaseName.set(other.databaseName.get());
+      databaseNameChanged.set(other.databaseNameChanged.get());
+    }
+    if (other.databaseDescriptionChanged.isAfter(databaseDescriptionChanged)) {
+      databaseDescription.set(other.databaseDescription.get());
+      databaseDescriptionChanged.set(other.databaseDescriptionChanged.get());
+    }
+    if (other.defaultUserNameChanged.isAfter(defaultUserNameChanged)) {
+      defaultUserName.set(other.defaultUserName.get());
+      defaultUserNameChanged.set(other.defaultUserNameChanged.get());
+    }
+    if (other.masterKeyChanged.isAfter(masterKeyChanged)) {
+      throw UnimplementedError(
+          'Other database changed master key. not supported.');
+    }
+    if (other.recycleBinChanged.isAfter(recycleBinChanged)) {
+      recycleBinEnabled.set(other.recycleBinEnabled.get());
+      recycleBinUUID.set(other.recycleBinUUID.get());
+      recycleBinChanged.set(other.recycleBinChanged.get());
+    }
+    final otherIsNewer = other.settingsChanged.isAfter(settingsChanged);
+
+    // merge custom data
+    for (final otherCustomDataEntry in other.customData.entries) {
+      if (otherIsNewer || !customData.containsKey(otherCustomDataEntry.key)) {
+        customData[otherCustomDataEntry.key] = otherCustomDataEntry.value;
+      }
+    }
+    // merge custom icons
+    for (final otherCustomIcon in other._customIcons.values) {
+      _customIcons[otherCustomIcon.uuid] ??= otherCustomIcon;
+    }
+
+    settingsChanged.set(other.settingsChanged.get());
+  }
 }
 
 class KdbxCustomIcon {
diff --git a/lib/src/kdbx_object.dart b/lib/src/kdbx_object.dart
index a50d08d..24b0b61 100644
--- a/lib/src/kdbx_object.dart
+++ b/lib/src/kdbx_object.dart
@@ -2,14 +2,16 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:typed_data';
 
-import 'package:kdbx/kdbx.dart';
 import 'package:kdbx/src/internal/extension_utils.dart';
 import 'package:kdbx/src/kdbx_file.dart';
+import 'package:kdbx/src/kdbx_format.dart';
 import 'package:kdbx/src/kdbx_group.dart';
+import 'package:kdbx/src/kdbx_meta.dart';
 import 'package:kdbx/src/kdbx_times.dart';
 import 'package:kdbx/src/kdbx_xml.dart';
 import 'package:logging/logging.dart';
 import 'package:meta/meta.dart';
+import 'package:quiver/iterables.dart';
 import 'package:uuid/uuid.dart';
 import 'package:uuid/uuid_util.dart';
 import 'package:xml/xml.dart';
@@ -36,6 +38,9 @@ mixin Changeable<T> {
 
   bool _isDirty = false;
 
+  /// allow recursive calls to [modify]
+  bool _isInModify = false;
+
   /// Called before the *first* modification (ie. before `isDirty` changes
   /// from false to true)
   @protected
@@ -49,14 +54,16 @@ mixin Changeable<T> {
   void onAfterModify() {}
 
   RET modify<RET>(RET Function() modify) {
-    if (_isDirty) {
+    if (_isDirty || _isInModify) {
       return modify();
     }
+    _isInModify = true;
     onBeforeModify();
     try {
       return modify();
     } finally {
       _isDirty = true;
+      _isInModify = false;
       onAfterModify();
       _controller.add(ChangeEvent(object: this as T, isDirty: _isDirty));
     }
@@ -102,9 +109,49 @@ abstract class KdbxNode with Changeable<KdbxNode> {
   }
 }
 
+extension IterableKdbxObject<T extends KdbxObject> on Iterable<T> {
+  T findByUuid(KdbxUuid uuid) =>
+      firstWhere((element) => element.uuid == uuid, orElse: () => null);
+}
+
+extension KdbxObjectInternal on KdbxObject {
+  List<KdbxSubNode> get objectNodes => [
+        icon,
+        customIconUuid,
+      ];
+
+  /// should only be used in internal code, used to clone
+  /// from one kdbx file into another. (like merging).
+  void forceSetUuid(KdbxUuid uuid) {
+    _uuid.set(uuid, force: true);
+  }
+
+  void assertSameUuid(KdbxObject other, String debugAction) {
+    if (uuid != other.uuid) {
+      throw StateError(
+          'Uuid of other object does not match current object for $debugAction');
+    }
+  }
+
+  void overwriteSubNodesFrom(OverwriteContext overwriteContext,
+      List<KdbxSubNode> myNodes, List<KdbxSubNode> otherNodes) {
+    for (final node in zip([myNodes, otherNodes])) {
+      final me = node[0];
+      final other = node[1];
+      if (me.set(other.get())) {
+        overwriteContext.trackChange(this, node: me.name);
+      }
+    }
+  }
+}
+
 abstract class KdbxObject extends KdbxNode {
-  KdbxObject.create(this.ctx, this.file, String nodeName, KdbxGroup parent)
-      : assert(ctx != null),
+  KdbxObject.create(
+    this.ctx,
+    this.file,
+    String nodeName,
+    KdbxGroup parent,
+  )   : assert(ctx != null),
         times = KdbxTimes.create(ctx),
         _parent = parent,
         super.create(nodeName) {
@@ -156,6 +203,13 @@ abstract class KdbxObject extends KdbxNode {
     file?.dirtyObject(this);
   }
 
+  bool wasModifiedAfter(KdbxObject other) => times.lastModificationTime
+      .get()
+      .isAfter(other.times.lastModificationTime.get());
+
+  bool wasMovedAfter(KdbxObject other) =>
+      times.locationChanged.get().isAfter(other.times.locationChanged.get());
+
   @override
   XmlElement toXml() {
     final el = super.toXml();
@@ -167,6 +221,8 @@ abstract class KdbxObject extends KdbxNode {
   void internalChangeParent(KdbxGroup parent) {
     modify(() => _parent = parent);
   }
+
+  void merge(MergeContext mergeContext, covariant KdbxObject other);
 }
 
 class KdbxUuid {
diff --git a/lib/src/kdbx_times.dart b/lib/src/kdbx_times.dart
index 08518d6..764ee5a 100644
--- a/lib/src/kdbx_times.dart
+++ b/lib/src/kdbx_times.dart
@@ -1,7 +1,8 @@
 import 'package:clock/clock.dart';
-import 'package:kdbx/kdbx.dart';
+import 'package:kdbx/src/kdbx_format.dart';
 import 'package:kdbx/src/kdbx_object.dart';
 import 'package:kdbx/src/kdbx_xml.dart';
+import 'package:quiver/iterables.dart';
 import 'package:xml/xml.dart';
 
 class KdbxTimes extends KdbxNode implements KdbxNodeContext {
@@ -38,4 +39,22 @@ class KdbxTimes extends KdbxNode implements KdbxNodeContext {
     accessedNow();
     lastModificationTime.set(clock.now().toUtc());
   }
+
+  List<KdbxSubNode> get _nodes => [
+        creationTime,
+        lastModificationTime,
+        lastAccessTime,
+        expiryTime,
+        expires,
+        usageCount,
+        locationChanged,
+      ];
+
+  void overwriteFrom(KdbxTimes other) {
+    for (final pair in zip([_nodes, other._nodes])) {
+      final me = pair[0];
+      final other = pair[1];
+      me.set(other.get());
+    }
+  }
 }
diff --git a/lib/src/kdbx_xml.dart b/lib/src/kdbx_xml.dart
index fceaca4..f432eac 100644
--- a/lib/src/kdbx_xml.dart
+++ b/lib/src/kdbx_xml.dart
@@ -2,7 +2,9 @@ import 'dart:convert';
 import 'dart:typed_data';
 
 import 'package:clock/clock.dart';
-import 'package:kdbx/kdbx.dart';
+import 'package:kdbx/src/kdbx_format.dart';
+import 'package:kdbx/src/kdbx_header.dart';
+import 'package:kdbx/src/kdbx_object.dart';
 import 'package:kdbx/src/utils/byte_utils.dart';
 import 'package:kdbx/src/kdbx_consts.dart';
 import 'package:meta/meta.dart';
@@ -58,7 +60,7 @@ abstract class KdbxSubNode<T> {
 
   T get();
 
-  void set(T value);
+  bool set(T value);
 
   void remove() {
     node.modify(() {
@@ -103,9 +105,9 @@ abstract class KdbxSubTextNode<T> extends KdbxSubNode<T> {
   }
 
   @override
-  void set(T value, {bool force = false}) {
+  bool set(T value, {bool force = false}) {
     if (get() == value && force != true) {
-      return;
+      return false;
     }
     node.modify(() {
       final el =
@@ -125,6 +127,7 @@ abstract class KdbxSubTextNode<T> extends KdbxSubNode<T> {
       el.children.add(XmlText(stringValue));
     });
     _onModify?.call();
+    return true;
   }
 
   @override
@@ -183,6 +186,30 @@ class IconNode extends KdbxSubTextNode<KdbxIcon> {
   String encode(KdbxIcon value) => value.index.toString();
 }
 
+class KdbxColor {
+  const KdbxColor._fromRgbCode(this._rgb) : assert(_rgb != null && _rgb != '');
+  const KdbxColor._nullColor() : _rgb = '';
+
+  factory KdbxColor.parse(String rgb) =>
+      rgb.isEmpty ? nullColor : KdbxColor._fromRgbCode(rgb);
+
+  static const nullColor = KdbxColor._nullColor();
+
+  final String _rgb;
+
+  bool get isNull => this == nullColor;
+}
+
+class ColorNode extends KdbxSubTextNode<KdbxColor> {
+  ColorNode(KdbxNode node, String name) : super(node, name);
+
+  @override
+  KdbxColor decode(String value) => KdbxColor.parse(value);
+
+  @override
+  String encode(KdbxColor value) => value.isNull ? '' : value._rgb;
+}
+
 class BooleanNode extends KdbxSubTextNode<bool> {
   BooleanNode(KdbxNode node, String name) : super(node, name);
 
@@ -210,6 +237,8 @@ class DateTimeUtcNode extends KdbxSubTextNode<DateTime> {
 
   KdbxReadWriteContext get _ctx => (node as KdbxNodeContext).ctx;
 
+  bool isAfter(DateTimeUtcNode other) => get().isAfter(other.get());
+
   void setToNow() {
     set(clock.now().toUtc());
   }
diff --git a/pubspec.yaml b/pubspec.yaml
index 64da110..aa02dd3 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -23,6 +23,7 @@ dependencies:
   path: '>=1.6.0 <2.0.0'
   quiver: '>=2.1.0 <3.0.0'
   archive: '>=2.0.13 <3.0.0'
+  supercharged_dart: '>=1.2.0 <2.0.0'
 
   collection: '>=1.14.0 <2.0.0'