+/*
+ "Everything you ever wanted to know about the default buttons" or "Why do we
+ have to do all this?"
+
+ In MSW the default button should be activated when the user presses Enter
+ and the current control doesn't process Enter itself somehow. This is
+ handled by ::DefWindowProc() (or maybe ::DefDialogProc()) using DM_SETDEFID
+ Another aspect of "defaultness" is that the default button has different
+ appearance: this is due to BS_DEFPUSHBUTTON style which is completely
+ separate from DM_SETDEFID stuff (!).
+
+ Final complication is that when a button is active, it should be the default
+ one, i.e. pressing Enter on a button always activates it and not another
+ one.
+
+ We handle this by maintaining a permanent and a temporary default items in
+ wxControlContainer (both may be NULL). When a button becomes the current
+ control (i.e. gets focus) it sets itself as the temporary default which
+ ensures that it has the right appearance and that Enter will be redirected
+ to it. When the button loses focus, it unsets the temporary default and so
+ the default item will be the permanent default -- that is the default button
+ if any had been set or none otherwise, which is just what we want.
+
+ Remark that we probably don't need to send DM_SETDEFID as we don't use
+ ::IsDialogMessage() (which relies on it) any longer but OTOH it probably
+ doesn't hurt neither.
+ */
+
+// set this button as the (permanently) default one in its panel