Improve wxDataViewModel::Cleared() documentation

Explain that this method can be useful not only when the model is
cleared.

interface/wx/dataview.h

@@ -52,6 +52,10 @@
     - wxDataViewModel::ItemsDeleted,
     - wxDataViewModel::ItemsChanged.
 
+    Note that Cleared() can be called for all changes involving many, or all,
+    of the model items and not only for deleting all of them (i.e. clearing the
+    model).
+
     This class maintains a list of wxDataViewModelNotifier which link this class
     to the specific implementations on the supported platforms so that e.g. calling
     wxDataViewModel::ValueChanged on this model will just call
@@ -129,8 +133,16 @@ public:
                      unsigned int col);
 
     /**
-        Called to inform the model that all data has been cleared.
+        Called to inform the model that all of its data has been changed.
-        The control will reread the data from the model again.
+
+        This method should be called if so many of the model items have
+        changed, that the control should just reread all of them, repopulating
+        itself entirely.
+
+        Note that, contrary to the name of the method, it doesn't necessarily
+        indicate that model has become empty -- although this is the right
+        method to call, rather than ItemsDeleted(), if it was indeed cleared,
+        which explains the origin of its name.
     */
     bool Cleared();