This method can be overwritten by widgets that want to provide accelerator functionality (Alt-key for example), but without interefering with normal ProcessKey behavior.
After keys are sent to the widgets on the current Container, all the widgets are processed and the key is passed to the widgets to allow some of them to process the keystroke as a cold-key.
This functionality is used, for example, by default buttons to act on the enter key. Processing this as a hot-key would prevent non-default buttons from consuming the enter keypress when they have the focus.