Document board change event listener code.

include/pcb_base_frame.h

@@ -382,8 +382,20 @@ public:
 
     virtual void ActivateGalCanvas() override;
 
+    /**
+     * Add \a aListener to post #EDA_EVT_BOARD_CHANGED command events to.
+     *
+     * @warning The caller is reponsible for removing any listeners that are no long valid.
+     *
+     * @note This only gets called when the board editor is in stand alone mode.  Changing
+     *       projects in the project manager closes the board editor when a new project is
+     *       loaded.
+     */
     void AddBoardChangeListener( wxEvtHandler* aListener );
 
+    /**
+     * Remove \a aListener to from the board changed listener list.
+     */
     void RemoveBoardChangeListener( wxEvtHandler* aListener );
 
 protected:

pcbnew/pcb_base_frame.cpp

@@ -234,6 +234,8 @@ void PCB_BASE_FRAME::SetBoard( BOARD* aBoard, PROGRESS_REPORTER* aReporter )
         {
             wxCHECK2( listener, continue );
 
+            // Use the windows variant when handling event messages in case there is any special
+            // event handler pre and/or post processing specific to windows.
             wxWindow* win = dynamic_cast<wxWindow*>( listener );
 
             if( win )