diff -r 3f949a4f2928 src/widget.cpp
--- a/src/widget.cpp	Sat Mar 07 19:08:30 2009 +0100
+++ b/src/widget.cpp	Sat Mar 07 19:27:02 2009 +0100
@@ -6,6 +6,7 @@
 #include "company_func.h"
 #include "gfx_func.h"
 #include "window_gui.h"
+#include "debug.h"
 
 #include "table/sprites.h"
 #include "table/strings.h"
@@ -1385,6 +1386,46 @@
 	return widgets;
 }
 
+/**
+ * Compare two widget arrays with each other, and report differences.
+ * @param orig Pointer to original widget array.
+ * @param gen  Pointer to generated widget array (from the nested widgets).
+ * @param report Report differences to stdout.
+ * @return Both widget arrays are equal.
+ */
+bool CompareWidgetArrays(const Widget *orig, const Widget *gen, bool report)
+{
+	int idx = 0;
+	bool same = true;
+
+	for(;;) {
+		const Widget *ow = orig + idx;
+		const Widget *gw = gen + idx;
+
+#define CHECK(var, prn) \
+	if (ow->var != gw->var) { \
+		same = false; \
+		if (report) DEBUG(misc, 1, "index %d, \"" #var "\" field: orig " prn ", gen " prn "\n", idx, ow->var, gw->var); \
+	}
+		CHECK(type, "%d")
+		CHECK(display_flags, "0x%x")
+		CHECK(colour, "%d")
+		CHECK(left, "%d")
+		CHECK(right, "%d")
+		CHECK(top, "%d")
+		CHECK(bottom, "%d")
+		CHECK(data, "%u")
+		CHECK(tooltips, "%u")
+#undef CHECK
+
+		if (ow->type == WWT_LAST || gw->type == WWT_LAST) break;
+
+		idx++;
+	}
+
+	return same;
+}
+
 /* == Conversion code from NWidgetPart array to NWidgetBase* tree == */
 
 /**
diff -r 3f949a4f2928 src/widget_type.h
--- a/src/widget_type.h	Sat Mar 07 19:08:30 2009 +0100
+++ b/src/widget_type.h	Sat Mar 07 19:27:02 2009 +0100
@@ -259,6 +259,7 @@
 };
 
 Widget *InitializeNWidgets(NWidgetBase *nwid, bool rtl = false);
+bool CompareWidgetArrays(const Widget *orig, const Widget *gen, bool report = true);
 
 /* == Nested widget parts == */
 
diff -r 3f949a4f2928 src/window.cpp
--- a/src/window.cpp	Sat Mar 07 19:08:30 2009 +0100
+++ b/src/window.cpp	Sat Mar 07 19:27:02 2009 +0100
@@ -54,7 +54,7 @@
 
 /** Window description constructor. */
 WindowDesc::WindowDesc(int16 lft, int16 ptop, int16 min_width, int16 min_height, int16 def_width, int16 def_height,
-			WindowClass wc, WindowClass pc, uint32 flgs, const Widget *widgs)
+			WindowClass wc, WindowClass pc, uint32 flgs, const Widget *widgs, const NWidgetPart *nwp, int16 nwl)
 {
 	this->left = lft;
 	this->top = ptop;
@@ -66,8 +66,45 @@
 	this->parent_cls = pc;
 	this->flags = flgs;
 	this->widgets = widgs;
+	this->nwid_parts = nwp;
+	this->nwid_length = nwl;
+	this->new_widgets = NULL;
 }
 
+/** Get widget array of the window description. */
+const Widget *WindowDesc::GetWidgets() const
+{
+	const bool RTL = false; // Direction of the language is left-to-right
+
+	/* If nested widgets are present, convert them to a widget array. */
+	if (this->nwid_parts != NULL && nwid_length > 0 && this->new_widgets == NULL) {
+		NWidgetContainer *nwid = MakeNWidgets(this->nwid_parts, this->nwid_length);
+		this->new_widgets = InitializeNWidgets(nwid, RTL);
+		delete nwid;
+	}
+
+	if (!RTL && this->widgets != NULL && this->new_widgets != NULL) {
+		/* There are two descriptions, compare them.
+		 * Comparing only makes sense when using a left-to-right language.
+		 */
+		bool ok = CompareWidgetArrays(this->widgets, this->new_widgets, false);
+		if (ok) {
+			DEBUG(misc, 1, "Nested widgets are equal");
+		} else {
+			DEBUG(misc, 0, "Nested widgets give different results");
+			CompareWidgetArrays(this->widgets, this->new_widgets, true);
+		}
+	}
+
+	const Widget *widgets = (this->widgets != NULL) ? this->widgets : this->new_widgets;
+	assert(widgets != NULL);
+	return widgets;
+}
+
+WindowDesc::~WindowDesc()
+{
+	if (this->new_widgets) free(this->new_widgets);
+}
 
 /**
  * Set the window that has the focus
@@ -1157,7 +1194,7 @@
 Window::Window(const WindowDesc *desc, WindowNumber window_number)
 {
 	Point pt = LocalGetWindowPlacement(desc, window_number);
-	this->Initialize(pt.x, pt.y, desc->minimum_width, desc->minimum_height, desc->cls, desc->widgets, window_number);
+	this->Initialize(pt.x, pt.y, desc->minimum_width, desc->minimum_height, desc->cls, desc->GetWidgets(), window_number);
 	this->desc_flags = desc->flags;
 }
 
diff -r 3f949a4f2928 src/window_gui.h
--- a/src/window_gui.h	Sat Mar 07 19:08:30 2009 +0100
+++ b/src/window_gui.h	Sat Mar 07 19:27:02 2009 +0100
@@ -41,18 +41,26 @@
 struct WindowDesc : ZeroedMemoryAllocator {
 
 	WindowDesc(int16 lft, int16 top, int16 min_width, int16 min_height, int16 def_width, int16 def_height,
-			WindowClass wc, WindowClass pc, uint32 flgs, const Widget *widgs);
+			WindowClass wc, WindowClass pc, uint32 flgs, const Widget *widgs,
+			const NWidgetPart *nwp = NULL, int16 nwl = 0);
 
-	int16 left;             ///< Prefered x position of left edge of the window, @see WindowDefaultPosition()
-	int16 top;              ///< Prefered y position of the top of the window, @see WindowDefaultPosition()
-	int16 minimum_width;    ///< Minimal width of the window
-	int16 minimum_height;   ///< Minimal height of the window
-	int16 default_width;    ///< Prefered initial width of the window
-	int16 default_height;   ///< Prefered initial height of the window
-	WindowClass cls;        ///< Class of the window, @see WindowClass
-	WindowClass parent_cls; ///< Class of the parent window, @see WindowClass
-	uint32 flags;           ///< Flags, @see WindowDefaultFlags
-	const Widget *widgets;  ///< List of widgets with their position and size for the window
+	~WindowDesc();
+
+	int16 left;                    ///< Prefered x position of left edge of the window. @see WindowDefaultPosition()
+	int16 top;                     ///< Prefered y position of the top of the window. @see WindowDefaultPosition()
+	int16 minimum_width;           ///< Minimal width of the window.
+	int16 minimum_height;          ///< Minimal height of the window.
+	int16 default_width;           ///< Prefered initial width of the window.
+	int16 default_height;          ///< Prefered initial height of the window.
+	WindowClass cls;               ///< Class of the window, @see WindowClass.
+	WindowClass parent_cls;        ///< Class of the parent window. @see WindowClass
+	uint32 flags;                  ///< Flags. @see WindowDefaultFlag.
+	const Widget *widgets;         ///< List of widgets with their position and size for the window.
+	const NWidgetPart *nwid_parts; ///< Nested widget parts describing the window.
+	int16 nwid_length;             ///< Length of the #nwid_parts array.
+	mutable Widget *new_widgets;   ///< Widgets generated from #nwid_parts.
+
+	const Widget *GetWidgets() const;
 };
 
 /**