public void preventTabFocus() {
        // com.google.gwt.user.client.ui.FocusWidget.onAttach replaces a tabIndex of -1 with 0
        // so use -2 to stop the help button having a tab index.
        getElement().setTabIndex(-2);
    }
Stop the help button being part of the tab index. Useful on forms where
you have a help button for each form group. The help is accessible
stroom-core-client-widget/src/main/java/stroom/widget/help/client/HelpButton.java