I recall the media release from BP about future titles ahead of the marriage of Edward and Sophie - then to be Wessex and now Edinburgh.

That notice said that any children "should not be given the style His or Her Royal Highness".

And it avoided use of Prince or Princess by stating they "would have courtesy titles as sons or daughters of an Earl".

I recall there was debate at the time about the "authority" of such a notice but in practice it did have the desired effect .