diff --git a/CMakeLists.txt b/CMakeLists.txt
index 15d69e0..ecf3f2b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -84,6 +84,7 @@ PRIVATE
     ui/platform/win/ui_window_win.h
     ui/platform/win/ui_utility_win.cpp
     ui/platform/win/ui_utility_win.h
+    ui/platform/ui_platform_window.cpp
     ui/platform/ui_platform_window.h
     ui/platform/ui_platform_utility.h
     ui/style/style_core.cpp
diff --git a/ui/platform/linux/ui_window_linux.cpp b/ui/platform/linux/ui_window_linux.cpp
index 8e2a83a..c98869a 100644
--- a/ui/platform/linux/ui_window_linux.cpp
+++ b/ui/platform/linux/ui_window_linux.cpp
@@ -9,7 +9,7 @@
 namespace Ui {
 namespace Platform {
 
-std::unique_ptr<BasicWindowHelper> CreateWindowHelper(
+std::unique_ptr<BasicWindowHelper> CreateSpecialWindowHelper(
 		not_null<RpWidget*> window) {
 	return nullptr;
 }
diff --git a/ui/platform/mac/ui_window_mac.h b/ui/platform/mac/ui_window_mac.h
index ab43e42..85af0e9 100644
--- a/ui/platform/mac/ui_window_mac.h
+++ b/ui/platform/mac/ui_window_mac.h
@@ -32,7 +32,6 @@ private:
 	void init();
 	void toggleCustomTitle(bool visible);
 
-	const not_null<RpWidget*> _window;
 	const std::unique_ptr<Private> _private;
 	const not_null<TitleWidget*> _title;
 	const not_null<RpWidget*> _body;
diff --git a/ui/platform/mac/ui_window_mac.mm b/ui/platform/mac/ui_window_mac.mm
index df9039f..f2a1837 100644
--- a/ui/platform/mac/ui_window_mac.mm
+++ b/ui/platform/mac/ui_window_mac.mm
@@ -132,13 +132,13 @@ Fn<void()> WindowHelper::Private::enforceStyleCallback() {
 }
 
 void WindowHelper::Private::initOpenGL() {
-	auto forceOpenGL = std::make_unique<QOpenGLWidget>(_owner->_window);
+	auto forceOpenGL = std::make_unique<QOpenGLWidget>(_owner->window());
 }
 
 void WindowHelper::Private::resolveWeakPointers() {
-	_owner->_window->createWinId();
+	_owner->window()->createWinId();
 
-	_nativeView = reinterpret_cast<NSView*>(_owner->_window->winId());
+	_nativeView = reinterpret_cast<NSView*>(_owner->window()->winId());
 	_nativeWindow = _nativeView ? [_nativeView window] : nullptr;
 
 	Ensures(_nativeWindow != nullptr);
@@ -189,14 +189,14 @@ void WindowHelper::Private::init() {
 }
 
 WindowHelper::WindowHelper(not_null<RpWidget*> window)
-: _window(window)
+: BasicWindowHelper(window)
 , _private(std::make_unique<Private>(this))
 , _title(_private->customTitleHeight()
 	? Ui::CreateChild<TitleWidget>(
-		_window.get(),
+		window.get(),
 		_private->customTitleHeight())
 	: nullptr)
-, _body(Ui::CreateChild<RpWidget>(_window.get())) {
+, _body(Ui::CreateChild<RpWidget>(window.get())) {
 	init();
 }
 
@@ -211,7 +211,7 @@ void WindowHelper::setTitle(const QString &title) {
 	if (_title) {
 		_title->setText(title);
 	}
-	_window->setWindowTitle(
+	window()->setWindowTitle(
 		(!_title || _title->isHidden()) ? title : QString());
 }
 
@@ -226,29 +226,29 @@ void WindowHelper::toggleCustomTitle(bool visible) {
 		return;
 	}
 	_title->setVisible(visible);
-	_window->setWindowTitle(visible ? QString() : _title->text());
+	window()->setWindowTitle(visible ? QString() : _title->text());
 }
 
 void WindowHelper::setMinimumSize(QSize size) {
-	_window->setMinimumSize(
+	window()->setMinimumSize(
 		size.width(),
 		(_title ? _title->height() : 0) + size.height());
 }
 
 void WindowHelper::setFixedSize(QSize size) {
-	_window->setFixedSize(
+	window()->setFixedSize(
 		size.width(),
 		(_title ? _title->height() : 0) + size.height());
 }
 
 void WindowHelper::setGeometry(QRect rect) {
-	_window->setGeometry(
+	window()->setGeometry(
 		rect.marginsAdded({ 0, (_title ? _title->height() : 0), 0, 0 }));
 }
 
 void WindowHelper::init() {
 	rpl::combine(
-		_window->sizeValue(),
+		window()->sizeValue(),
 		_title->heightValue(),
 		_title->shownValue()
 	) | rpl::start_with_next([=](QSize size, int titleHeight, bool shown) {
@@ -263,7 +263,7 @@ void WindowHelper::init() {
 	}, _body->lifetime());
 }
 
-std::unique_ptr<BasicWindowHelper> CreateWindowHelper(
+std::unique_ptr<BasicWindowHelper> CreateSpecialWindowHelper(
 		not_null<RpWidget*> window) {
 	return std::make_unique<WindowHelper>(window);
 }
diff --git a/ui/platform/ui_platform_window.cpp b/ui/platform/ui_platform_window.cpp
new file mode 100644
index 0000000..9e38667
--- /dev/null
+++ b/ui/platform/ui_platform_window.cpp
@@ -0,0 +1,77 @@
+// This file is part of Desktop App Toolkit,
+// a set of libraries for developing nice desktop applications.
+//
+// For license and copyright information please follow this link:
+// https://github.com/desktop-app/legal/blob/master/LEGAL
+//
+#include "ui/platform/ui_platform_window.h"
+
+#include "ui/rp_widget.h"
+
+#include <QtGui/QWindow>
+#include <QtGui/QtEvents>
+
+namespace Ui {
+namespace Platform {
+
+BasicWindowHelper::BasicWindowHelper(not_null<RpWidget*> window)
+: _window(window) {
+}
+
+not_null<RpWidget*> BasicWindowHelper::body() {
+	return _window;
+}
+
+void BasicWindowHelper::setTitle(const QString &title) {
+	_window->setWindowTitle(title);
+}
+
+void BasicWindowHelper::setTitleStyle(const style::WindowTitle &st) {
+}
+
+void BasicWindowHelper::setMinimumSize(QSize size) {
+	_window->setMinimumSize(size);
+}
+
+void BasicWindowHelper::setFixedSize(QSize size) {
+	_window->setFixedSize(size);
+}
+
+void BasicWindowHelper::setGeometry(QRect rect) {
+	_window->setGeometry(rect);
+}
+
+void BasicWindowHelper::setBodyTitleArea(Fn<bool(QPoint)> testMethod) {
+	Expects(!_bodyTitleAreaTestMethod);
+
+	if (!testMethod) {
+		return;
+	}
+	_bodyTitleAreaTestMethod = std::move(testMethod);
+	if (customBodyTitleAreaHandling()) {
+		return;
+	}
+	body()->events() | rpl::start_with_next([=](not_null<QEvent*> e) {
+		if (e->type() == QEvent::MouseButtonDblClick) {
+			if (bodyTitleAreaHit(static_cast<QMouseEvent*>(e.get())->pos())) {
+				const auto state = _window->windowState();
+				if (state & Qt::WindowMaximized) {
+					_window->setWindowState(state & ~Qt::WindowMaximized);
+				} else {
+					_window->setWindowState(state | Qt::WindowMaximized);
+				}
+			}
+		} else if (e->type() == QEvent::MouseMove) {
+			const auto mouseEvent = static_cast<QMouseEvent*>(e.get());
+			if (bodyTitleAreaHit(mouseEvent->pos())
+				&& (mouseEvent->buttons() & Qt::LeftButton)) {
+#if QT_VERSION >= QT_VERSION_CHECK(5, 15, 0) || defined DESKTOP_APP_QT_PATCHED
+				_window->windowHandle()->startSystemMove();
+#endif // Qt >= 5.15 || DESKTOP_APP_QT_PATCHED
+			}
+		}
+	}, body()->lifetime());
+}
+
+} // namespace Platform
+} // namespace Ui
diff --git a/ui/platform/ui_platform_window.h b/ui/platform/ui_platform_window.h
index 4fff950..533875f 100644
--- a/ui/platform/ui_platform_window.h
+++ b/ui/platform/ui_platform_window.h
@@ -18,18 +18,45 @@ namespace Platform {
 
 class BasicWindowHelper {
 public:
-	[[nodiscard]] virtual not_null<RpWidget*> body() = 0;
-	virtual void setTitle(const QString &title) = 0;
-	virtual void setTitleStyle(const style::WindowTitle &st) = 0;
-	virtual void setMinimumSize(QSize size) = 0;
-	virtual void setFixedSize(QSize size) = 0;
-	virtual void setGeometry(QRect rect) = 0;
+	explicit BasicWindowHelper(not_null<RpWidget*> window);
+
+	[[nodiscard]] virtual not_null<RpWidget*> body();
+	virtual void setTitle(const QString &title);
+	virtual void setTitleStyle(const style::WindowTitle &st);
+	virtual void setMinimumSize(QSize size);
+	virtual void setFixedSize(QSize size);
+	virtual void setGeometry(QRect rect);
 	virtual ~BasicWindowHelper() = default;
 
+	void setBodyTitleArea(Fn<bool(QPoint)> testMethod);
+
+protected:
+	[[nodiscard]] not_null<RpWidget*> window() const {
+		return _window;
+	}
+	[[nodiscard]] bool bodyTitleAreaHit(QPoint point) const {
+		return _bodyTitleAreaTestMethod && _bodyTitleAreaTestMethod(point);
+	}
+	[[nodiscard]] virtual bool customBodyTitleAreaHandling() {
+		return false;
+	}
+
+private:
+	const not_null<RpWidget*> _window;
+	Fn<bool(QPoint)> _bodyTitleAreaTestMethod;
+
 };
 
-[[nodiscard]] std::unique_ptr<BasicWindowHelper> CreateWindowHelper(
+[[nodiscard]] std::unique_ptr<BasicWindowHelper> CreateSpecialWindowHelper(
 	not_null<RpWidget*> window);
 
+[[nodiscard]] inline std::unique_ptr<BasicWindowHelper> CreateWindowHelper(
+		not_null<RpWidget*> window) {
+	if (auto special = CreateSpecialWindowHelper(window)) {
+		return special;
+	}
+	return std::make_unique<BasicWindowHelper>(window);
+}
+
 } // namespace Platform
 } // namespace Ui
diff --git a/ui/platform/win/ui_window_win.cpp b/ui/platform/win/ui_window_win.cpp
index 934edd6..3428e1e 100644
--- a/ui/platform/win/ui_window_win.cpp
+++ b/ui/platform/win/ui_window_win.cpp
@@ -93,11 +93,11 @@ bool WindowHelper::NativeFilter::nativeEventFilter(
 }
 
 WindowHelper::WindowHelper(not_null<RpWidget*> window)
-: _window(window)
-, _handle(GetWindowHandle(_window))
-, _title(Ui::CreateChild<TitleWidget>(_window.get()))
-, _body(Ui::CreateChild<RpWidget>(_window.get()))
-, _shadow(_window, st::windowShadowFg->c) {
+: BasicWindowHelper(window)
+, _handle(GetWindowHandle(window))
+, _title(Ui::CreateChild<TitleWidget>(window.get()))
+, _body(Ui::CreateChild<RpWidget>(window.get()))
+, _shadow(window, st::windowShadowFg->c) {
 	Expects(_handle != nullptr);
 
 	GetNativeFilter()->registerWindow(_handle, this);
@@ -114,7 +114,7 @@ not_null<RpWidget*> WindowHelper::body() {
 
 void WindowHelper::setTitle(const QString &title) {
 	_title->setText(title);
-	_window->setWindowTitle(title);
+	window()->setWindowTitle(title);
 }
 
 void WindowHelper::setTitleStyle(const style::WindowTitle &st) {
@@ -122,27 +122,27 @@ void WindowHelper::setTitleStyle(const style::WindowTitle &st) {
 }
 
 void WindowHelper::setMinimumSize(QSize size) {
-	_window->setMinimumSize(size.width(), _title->height() + size.height());
+	window()->setMinimumSize(size.width(), _title->height() + size.height());
 }
 
 void WindowHelper::setFixedSize(QSize size) {
-	_window->setFixedSize(size.width(), _title->height() + size.height());
+	window()->setFixedSize(size.width(), _title->height() + size.height());
 	_title->setResizeEnabled(false);
 	_shadow.setResizeEnabled(false);
 }
 
 void WindowHelper::setGeometry(QRect rect) {
-	_window->setGeometry(rect.marginsAdded({ 0, _title->height(), 0, 0 }));
+	window()->setGeometry(rect.marginsAdded({ 0, _title->height(), 0, 0 }));
 }
 
 void WindowHelper::init() {
 	style::PaletteChanged(
 	) | rpl::start_with_next([=] {
 		_shadow.setColor(st::windowShadowFg->c);
-	}, _window->lifetime());
+	}, window()->lifetime());
 
 	rpl::combine(
-		_window->sizeValue(),
+		window()->sizeValue(),
 		_title->heightValue()
 	) | rpl::start_with_next([=](QSize size, int titleHeight) {
 		_body->setGeometry(
@@ -165,14 +165,14 @@ void WindowHelper::init() {
 	const auto handleStateChanged = [=](Qt::WindowState state) {
 		updateSystemMenu(state);
 		if (fixedSize() && (state & Qt::WindowMaximized)) {
-			crl::on_main(_window.get(), [=] {
-				_window->setWindowState(
-					_window->windowState() & ~Qt::WindowMaximized);
+			crl::on_main(window().get(), [=] {
+				window()->setWindowState(
+					window()->windowState() & ~Qt::WindowMaximized);
 			});
 		}
 	};
 	Ui::Connect(
-		_window->windowHandle(),
+		window()->windowHandle(),
 		&QWindow::windowStateChanged,
 		handleStateChanged);
 }
@@ -186,14 +186,14 @@ bool WindowHelper::handleNativeEvent(
 
 	case WM_ACTIVATE: {
 		if (LOWORD(wParam) == WA_CLICKACTIVE) {
-			Ui::MarkInactivePress(_window, true);
+			Ui::MarkInactivePress(window(), true);
 		}
 		if (LOWORD(wParam) != WA_INACTIVE) {
 			_shadow.update(WindowShadow::Change::Activate);
 		} else {
 			_shadow.update(WindowShadow::Change::Deactivate);
 		}
-		_window->update();
+		window()->update();
 	} return false;
 
 	case WM_NCPAINT: {
@@ -267,14 +267,14 @@ bool WindowHelper::handleNativeEvent(
 			|| wParam == SIZE_RESTORED
 			|| wParam == SIZE_MINIMIZED) {
 			if (wParam != SIZE_RESTORED
-				|| _window->windowState() != Qt::WindowNoState) {
+				|| window()->windowState() != Qt::WindowNoState) {
 				Qt::WindowState state = Qt::WindowNoState;
 				if (wParam == SIZE_MAXIMIZED) {
 					state = Qt::WindowMaximized;
 				} else if (wParam == SIZE_MINIMIZED) {
 					state = Qt::WindowMinimized;
 				}
-				emit _window->windowHandle()->windowStateChanged(state);
+				emit window()->windowHandle()->windowStateChanged(state);
 			}
 			updateMargins();
 			const auto changes = (wParam == SIZE_MINIMIZED
@@ -310,10 +310,12 @@ bool WindowHelper::handleNativeEvent(
 		const auto mapped = QPoint(
 			p.x - r.left + _marginsDelta.left(),
 			p.y - r.top + _marginsDelta.top());
-		if (!_window->rect().contains(mapped)) {
+		if (!window()->rect().contains(mapped)) {
 			*result = HTTRANSPARENT;
 		} else if (!_title->geometry().contains(mapped)) {
-			*result = HTCLIENT;
+			*result = bodyTitleAreaHit(mapped - QPoint(0, _title->height()))
+				? HTCAPTION
+				: HTCLIENT;
 		} else switch (_title->hitTest(_title->pos() + mapped)) {
 		case HitTestResult::Client:
 		case HitTestResult::SysButton:   *result = HTCLIENT; break;
@@ -338,7 +340,7 @@ bool WindowHelper::handleNativeEvent(
 	case WM_SYSCOMMAND: {
 		if (wParam == SC_MOUSEMENU && !fixedSize()) {
 			POINTS p = MAKEPOINTS(lParam);
-			updateSystemMenu(_window->windowHandle()->windowState());
+			updateSystemMenu(window()->windowHandle()->windowState());
 			TrackPopupMenu(
 				_menu,
 				TPM_LEFTALIGN | TPM_TOPALIGN | TPM_LEFTBUTTON,
@@ -357,19 +359,19 @@ bool WindowHelper::handleNativeEvent(
 		const auto command = LOWORD(wParam);
 		switch (command) {
 		case SC_CLOSE:
-			_window->close();
+			window()->close();
 			return true;
 		case SC_MINIMIZE:
-			_window->setWindowState(
-				_window->windowState() | Qt::WindowMinimized);
+			window()->setWindowState(
+				window()->windowState() | Qt::WindowMinimized);
 			return true;
 		case SC_MAXIMIZE:
 			if (!fixedSize()) {
-				_window->setWindowState(Qt::WindowMaximized);
+				window()->setWindowState(Qt::WindowMaximized);
 			}
 			return true;
 		case SC_RESTORE:
-			_window->setWindowState(Qt::WindowNoState);
+			window()->setWindowState(Qt::WindowNoState);
 			return true;
 		}
 	} return true;
@@ -379,7 +381,7 @@ bool WindowHelper::handleNativeEvent(
 }
 
 bool WindowHelper::fixedSize() const {
-	return _window->minimumSize() == _window->maximumSize();
+	return window()->minimumSize() == window()->maximumSize();
 }
 
 void WindowHelper::updateMargins() {
@@ -444,14 +446,14 @@ void WindowHelper::updateMargins() {
 
 	if (const auto native = QGuiApplication::platformNativeInterface()) {
 		native->setWindowProperty(
-			_window->windowHandle()->handle(),
+			window()->windowHandle()->handle(),
 			"WindowsCustomMargins",
 			QVariant::fromValue<QMargins>(margins));
 	}
 }
 
 void WindowHelper::updateSystemMenu() {
-	updateSystemMenu(_window->windowHandle()->windowState());
+	updateSystemMenu(window()->windowHandle()->windowState());
 }
 
 void WindowHelper::updateSystemMenu(Qt::WindowState state) {
@@ -518,7 +520,7 @@ HWND GetWindowHandle(not_null<RpWidget*> widget) {
 		window));
 }
 
-std::unique_ptr<BasicWindowHelper> CreateWindowHelper(
+std::unique_ptr<BasicWindowHelper> CreateSpecialWindowHelper(
 		not_null<RpWidget*> window) {
 	return std::make_unique<WindowHelper>(window);
 }
diff --git a/ui/platform/win/ui_window_win.h b/ui/platform/win/ui_window_win.h
index ff88284..d8003bc 100644
--- a/ui/platform/win/ui_window_win.h
+++ b/ui/platform/win/ui_window_win.h
@@ -32,6 +32,10 @@ private:
 	class NativeFilter;
 	friend class NativeFilter;
 
+	bool customBodyTitleAreaHandling() override {
+		return true;
+	}
+
 	void init();
 	void updateMargins();
 	void updateSystemMenu();
@@ -45,7 +49,6 @@ private:
 
 	static not_null<NativeFilter*> GetNativeFilter();
 
-	const not_null<RpWidget*> _window;
 	const HWND _handle = nullptr;
 	const not_null<TitleWidget*> _title;
 	const not_null<RpWidget*> _body;
diff --git a/ui/widgets/window.cpp b/ui/widgets/window.cpp
index 113fb7f..2b8538e 100644
--- a/ui/widgets/window.cpp
+++ b/ui/widgets/window.cpp
@@ -13,55 +13,43 @@ namespace Ui {
 Window::Window(QWidget *parent)
 : RpWidget(parent)
 , _helper(Platform::CreateWindowHelper(this)) {
+	Expects(_helper != nullptr);
+
 	hide();
 }
 
 Window::~Window() = default;
 
 not_null<RpWidget*> Window::body() {
-	return _helper ? _helper->body() : this;
+	return _helper->body();
 }
 
 not_null<const RpWidget*> Window::body() const {
-	return _helper ? _helper->body().get() : this;
+	return _helper->body().get();
 }
 
 void Window::setTitle(const QString &title) {
-	if (_helper) {
-		_helper->setTitle(title);
-	} else {
-		setWindowTitle(title);
-	}
+	_helper->setTitle(title);
 }
 
 void Window::setTitleStyle(const style::WindowTitle &st) {
-	if (_helper) {
-		_helper->setTitleStyle(st);
-	}
+	_helper->setTitleStyle(st);
 }
 
 void Window::setMinimumSize(QSize size) {
-	if (_helper) {
-		_helper->setMinimumSize(size);
-	} else {
-		RpWidget::setMinimumSize(size);
-	}
+	_helper->setMinimumSize(size);
 }
 
 void Window::setFixedSize(QSize size) {
-	if (_helper) {
-		_helper->setFixedSize(size);
-	} else {
-		RpWidget::setFixedSize(size);
-	}
+	_helper->setFixedSize(size);
 }
 
 void Window::setGeometry(QRect rect) {
-	if (_helper) {
-		_helper->setGeometry(rect);
-	} else {
-		RpWidget::setGeometry(rect);
-	}
+	_helper->setGeometry(rect);
+}
+
+void Window::setBodyTitleArea(Fn<bool(QPoint)> testMethod) {
+	_helper->setBodyTitleArea(std::move(testMethod));
 }
 
 } // namespace Ui
diff --git a/ui/widgets/window.h b/ui/widgets/window.h
index 7a96a6a..3d2c6a8 100644
--- a/ui/widgets/window.h
+++ b/ui/widgets/window.h
@@ -30,6 +30,7 @@ public:
 	void setMinimumSize(QSize size);
 	void setFixedSize(QSize size);
 	void setGeometry(QRect rect);
+	void setBodyTitleArea(Fn<bool(QPoint)> testMethod);
 
 private:
 	const std::unique_ptr<Platform::BasicWindowHelper> _helper;