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diff --git a/xfa/fwl/README.md b/xfa/fwl/README.md
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+xfa/fwl is a Widget Library for XFA Forms.
+
+CFWL_Widget is the base class that widget classes extend. The derived widget
+classes are both controllers and renderers for each widget. The hierarchy is:
+
+* CFWL_Widget
+    * CFWL_Form
+        * CFWL_FormProxy
+            * CFWL_ComboBoxProxy
+    * CFWL_Caret
+    * CFWL_CheckBox
+    * CFWL_ComboBox
+    * CFWL_DateTimePicker
+    * CFWL_Edit
+        * CFWL_Barcode
+        * CFWL_ComboEdit
+        * CFWL_DateTimeEdit
+    * CFWL_ListBox
+        * CFWL_ComboList
+    * CFWL_MonthCalendar
+    * CFWL_PictureBox
+    * CFWL_PushButton
+    * CFWL_ScrollBar
+    * CFWL_SpinButton
+
+These CFWL widgets are instantiated by and closely related to the CXFA classes
+in the xfa/fxfa directory. See xfa/fxfa/README.md.
+
+CFWL_Widget implements IFWL_WidgetDelegate through which it receives messages,
+events and draw calls.
+
+Messages consist of user input for a widget to handle. Each type of message is
+identified by an enum value in Message::Type and has its own class derived from
+the base CFWL_Message.
+
+* CFWL_Message
+    * CFWL_MessageKey
+    * CFWL_MessageKillFocus
+    * CFWL_MessageMouse
+    * CFWL_MessageMouseWheel
+    * CFWL_MessageSetFocus
+
+Events are originated in the widgets and are then handled by other CFWL_Widget
+and CXFA classes.
+
+* CFWL_Event
+    * CFWL_EventCheckWord
+    * CFWL_EventMouse
+    * CFWL_EventScroll
+    * CFWL_EventSelectChanged
+    * CFWL_EventTextChanged
+    * CFWL_EventValidate
+
+The widgets use IFWL_ThemeProvider for rendering everything, calling
+DrawBackground() and DrawText() and passing many options in their parameters,
+respectively of types CFWL_ThemeBackground and CFWL_ThemeText. See
+xfa/fwl/theme/README.md.
+
diff --git a/xfa/fwl/theme/README.md b/xfa/fwl/theme/README.md
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+xfa/fwl/theme contains code for rendering XFA widgets.
+
+TP stands for Theme Part.
+
+CFWL_WidgetTP contains much of the code common to more than one widget.
+
+The other CFWL_TP classes derive from it and know how to draw the pieces
+specific to their respective widget.
+
+The inheritance hierarchy for this directory is:
+
+* CFWL_WidgetTP
+    * CFWL_BarcodeTP
+    * CFWL_CaretTP
+    * CFWL_CheckboxTP
+    * CFWL_ComboBowTP
+    * CFWL_DateTimePickerTP
+    * CFWL_EditTP
+    * CFWL_ListBoxTP
+    * CFWL_MonthCalendarTP
+    * CFWL_PictureBoxTP
+    * CFWL_PushButtonTP
+    * CFWL_ScrollBarTP
+
+All these widget TP classes are composed into CXFA_FWLTheme, which implements
+IFWL_ThemeProvider (and is the only class that does). CXFA_FWLTheme receives
+DrawBackground() calls from CFWL widgets to draw themselves and routes them to
+the TP (Theme Part) corresponding to that widget.
+