I have a widget on a page.
It's wrapped in HTML by the silverstripe/sappire/templates/WidgetHolder.ss file which contains:
I would prefer the title to be an h2 element rather than an h3 element.
I copied the above, changing h3 to h2 and put it in silverstripe/themes/mytheme/templates/Includes as per this page http://doc.silverstripe.org/doku.php?id=widgets
You can override the WidgetHolder.ss and Widget.ss templates in your theme too by adding WidgetHolder and Widget templates to themes/myThemeName/templates/Includes/
but it didn't work.
If I delete the core sapphire file (silverstripe/sappire/templates/WidgetHolder.ss) it works fine but obviously I don't want to do that because it will break following an update to the core sapphire files.