diff --git a/dlanguilib.visualdproj b/dlanguilib.visualdproj
index 2c6e1ed0..3de7f3f8 100644
--- a/dlanguilib.visualdproj
+++ b/dlanguilib.visualdproj
@@ -381,6 +381,7 @@
      <File path="src\dlangui\widgets\appframe.d" />
      <File path="src\dlangui\widgets\combobox.d" />
      <File path="src\dlangui\widgets\controls.d" />
+     <File path="src\dlangui\widgets\docks.d" />
      <File path="src\dlangui\widgets\editors.d" />
      <File path="src\dlangui\widgets\grid.d" />
      <File path="src\dlangui\widgets\layouts.d" />
diff --git a/res/theme_default.xml b/res/theme_default.xml
index bb6e3049..61b0ffb2 100644
--- a/res/theme_default.xml
+++ b/res/theme_default.xml
@@ -223,6 +223,39 @@
         padding="4,4,4,4"
 	layoutWeight="0"
         />
+    <style id="DOCK_HOST"
+        backgroundColor="#303080"
+        layoutWidth="FILL_PARENT"
+        layoutHeight="FILL_PARENT"
+        padding="4,4,4,4"
+        margins="4,4,4,4"
+        />
+    <style id="DOCK_WINDOW"
+        backgroundColor="#D0D0FF"
+        layoutWidth="FILL_PARENT"
+        layoutHeight="FILL_PARENT"
+        padding="1,1,1,1"
+        margins="4,4,4,4"
+        />
+    <style id="DOCK_WINDOW_CAPTION"
+        backgroundColor="#202060"
+        layoutWidth="FILL_PARENT"
+        layoutHeight="WRAP_CONTENT"
+        padding="1,1,1,1"
+        />
+    <style id="DOCK_WINDOW_CAPTION_LABEL"
+        textColor="#FFFFFF"
+        layoutWidth="FILL_PARENT"
+        layoutHeight="WRAP_CONTENT"
+        padding="2,2,2,2"
+        align="Left|VCenter"
+        />
+    <style id="DOCK_WINDOW_BODY"
+        backgroundColor="#FFFFFF"
+        layoutWidth="FILL_PARENT"
+        layoutHeight="FILL_PARENT"
+        padding="1,1,1,1"
+        />
     <style id="TREE_ITEM"
         padding="2,2,2,2"
         margins="0,0,0,0"
diff --git a/src/dlangui/all.d b/src/dlangui/all.d
index 5d13a434..7fe2d2c7 100644
--- a/src/dlangui/all.d
+++ b/src/dlangui/all.d
@@ -69,6 +69,7 @@ public import dlangui.widgets.combobox;
 public import dlangui.widgets.popup;
 public import dlangui.widgets.appframe;
 public import dlangui.widgets.statusline;
+public import dlangui.widgets.docks;
 public import dlangui.platforms.common.platform;
 
 // some useful imports from Phobos
diff --git a/src/dlangui/core/collections.d b/src/dlangui/core/collections.d
index 50c6d574..09f37eaf 100644
--- a/src/dlangui/core/collections.d
+++ b/src/dlangui/core/collections.d
@@ -258,6 +258,8 @@ struct ObjectList(T) {
     }
     /** find child index for item, return -1 if not found */
     int indexOf(T item) {
+        if (item is null)
+            return -1;
         for (int i = 0; i < _count; i++)
             if (_list[i] == item)
                 return i;
@@ -287,6 +289,21 @@ struct ObjectList(T) {
         _list[index] = item;
         destroy(old);
     }
+    /** Replace item with another value, destroy old value. */
+    void replace(T newItem, T oldItem) {
+        int idx = indexOf(oldItem);
+        if (newItem is null) {
+            if (idx >= 0) {
+                T item = remove(idx);
+                destroy(item);
+            }
+        } else {
+            if (idx >= 0)
+                replace(newItem, idx);
+            else
+                add(newItem);
+        }
+    }
     /** remove and destroy all items */
     void clear() {
         for (int i = 0; i < _count; i++) {
diff --git a/src/dlangui/widgets/docks.d b/src/dlangui/widgets/docks.d
new file mode 100644
index 00000000..eaf5be39
--- /dev/null
+++ b/src/dlangui/widgets/docks.d
@@ -0,0 +1,84 @@
+module dlangui.widgets.docks;
+
+import dlangui.widgets.layouts;
+import dlangui.widgets.controls;
+
+class DockHost : WidgetGroupDefaultDrawing {
+    protected Widget _bodyWidget;
+    @property Widget bodyWidget() { return _bodyWidget; }
+    @property void bodyWidget(Widget widget) { 
+        _children.replace(_bodyWidget, widget);
+        _bodyWidget = widget;
+        _bodyWidget.layoutWidth(FILL_PARENT).layoutHeight(FILL_PARENT);
+    }
+
+    this() {
+        super("DOCK_HOST");
+    }
+}
+
+enum DockAlignment {
+    Left,
+    Right,
+    Top,
+    Bottom
+}
+
+class DockWindow : VerticalLayout {
+
+    protected Widget _bodyWidget;
+    @property Widget bodyWidget() { return _bodyWidget; }
+    @property void bodyWidget(Widget widget) { 
+        _children.replace(_bodyWidget, widget);
+        _bodyWidget = widget;
+        _bodyWidget.layoutWidth(FILL_PARENT).layoutHeight(FILL_PARENT);
+    }
+
+    protected DockAlignment _dockAlignment;
+    protected HorizontalLayout _captionLayout;
+    protected TextWidget _caption;
+    protected ImageButton _closeButton;
+    this(string ID) {
+        super(ID);
+        init();
+    }
+    protected bool onCloseButtonClick(Widget source) {
+        return true;
+    }
+    protected void init() {
+
+        styleId = STYLE_DOCK_WINDOW;
+
+        _captionLayout = new HorizontalLayout("DOCK_WINDOW_CAPTION_PANEL");
+        _captionLayout.layoutWidth(FILL_PARENT).layoutHeight(WRAP_CONTENT);
+        _captionLayout.styleId = STYLE_DOCK_WINDOW_CAPTION;
+
+        uint bcolor = _captionLayout.backgroundColor;
+        Log.d("caption layout back color=", bcolor);
+
+        //_captionLayout.backgroundColor = 0x204060;
+
+        _caption = new TextWidget("DOCK_WINDOW_CAPTION");
+        _caption.styleId = STYLE_DOCK_WINDOW_CAPTION_LABEL;
+
+        _closeButton = new ImageButton("DOCK_WINDOW_CAPTION_CLOSE_BUTTON");
+        _closeButton.styleId = STYLE_BUTTON_TRANSPARENT;
+        _closeButton.drawableId = "close";
+		_closeButton.trackHover = true;
+        _closeButton.onClickListener = &onCloseButtonClick;
+
+        _captionLayout.addChild(_caption);
+        _captionLayout.addChild(_closeButton);
+
+        _bodyWidget = createBodyWidget();
+        _bodyWidget.styleId = STYLE_DOCK_WINDOW_BODY;
+        //_bodyWidget.backgroundColor = 0xFFFFFF;
+        //_bodyWidget.layoutWidth(FILL_PARENT).layoutHeight(FILL_PARENT);
+
+        addChild(_captionLayout);
+        addChild(_bodyWidget);
+    }
+    protected Widget createBodyWidget() {
+        return new Widget("DOCK_WINDOW_BODY");
+    }
+}
diff --git a/src/dlangui/widgets/statusline.d b/src/dlangui/widgets/statusline.d
index 13a0fce1..849069ae 100644
--- a/src/dlangui/widgets/statusline.d
+++ b/src/dlangui/widgets/statusline.d
@@ -34,6 +34,7 @@ class StatusLine : HorizontalLayout {
     void init() {
         _defStatus = new TextWidget("STATUS_LINE_TEXT");
         _defStatus.layoutWidth(FILL_PARENT);
+        _defStatus.text = "DLANGUI"d;
         addChild(_defStatus);
     }
     /// set text to show in status line in specific panel
diff --git a/src/dlangui/widgets/styles.d b/src/dlangui/widgets/styles.d
index 03da2b7a..81448d01 100644
--- a/src/dlangui/widgets/styles.d
+++ b/src/dlangui/widgets/styles.d
@@ -119,6 +119,15 @@ immutable string STYLE_COMBO_BOX_BODY = "COMBO_BOX_BODY";
 /// standard style id for app frame status line
 immutable string STYLE_STATUS_LINE = "STATUS_LINE";
 
+/// standard style id for dock window caption
+immutable string STYLE_DOCK_WINDOW_CAPTION = "DOCK_WINDOW_CAPTION";
+/// standard style id for dock window
+immutable string STYLE_DOCK_WINDOW = "DOCK_WINDOW";
+/// standard style id for dock window caption label
+immutable string STYLE_DOCK_WINDOW_CAPTION_LABEL = "DOCK_WINDOW_CAPTION_LABEL";
+/// standard style id for dock window body
+immutable string STYLE_DOCK_WINDOW_BODY = "DOCK_WINDOW_BODY";
+
 // Layout size constants
 /// layout option, to occupy all available place
 immutable int FILL_PARENT = int.max - 1;
@@ -737,6 +746,9 @@ class Theme : Style {
 	
 	~this() {
 		//Log.d("Theme destructor");
+        if (unknownStyleIds.length > 0) {
+            Log.e("Unknown style statistics: ", unknownStyleIds);
+        }
 		foreach(ref Style item; _byId) {
 			destroy(item);
 			item = null;
@@ -817,10 +829,21 @@ class Theme : Style {
 		return style;
 	}
 
+    /// to track unknown styles refernced from code
+    int[string] unknownStyleIds;
 	/// find style by id, returns theme if not style with specified ID is not found
 	@property Style get(string id) {
-		if (id !is null && id in _byId)
+        if (id is null)
+            return this;
+		if (id in _byId)
 			return _byId[id];
+        // track unknown style ID references
+        if (id in unknownStyleIds)
+            unknownStyleIds[id] = unknownStyleIds[id] + 1;
+        else {
+            Log.e("Unknown style ID requested: ", id);
+            unknownStyleIds[id] = 1;
+        }
 		return this;
 	}
 	
@@ -1085,10 +1108,16 @@ int decodeLayoutDimension(string s) {
 
 /// load style attributes from XML element
 bool loadStyleAttributes(Style style, Element elem, bool allowStates) {
+    //Log.d("Theme: loadStyleAttributes ", style.id, " ", elem.tag.attr);
 	if ("backgroundImageId" in elem.tag.attr)
 		style.backgroundImageId = elem.tag.attr["backgroundImageId"];
-	if ("backgroundColor" in elem.tag.attr)
-		style.backgroundColor = decodeHexColor(elem.tag.attr["backgroundColor"]);
+	if ("backgroundColor" in elem.tag.attr) {
+        uint col = decodeHexColor(elem.tag.attr["backgroundColor"]);
+		style.backgroundColor = col;
+        //Log.d("    background color=", col);
+    } else {
+        //Log.d("    no background color attr");
+    }
 	if ("textColor" in elem.tag.attr)
 		style.textColor = decodeHexColor(elem.tag.attr["textColor"]);
 	if ("margins" in elem.tag.attr)