Please excuse the long title: it took me a while to figure this one out, so I want to make sure that other people can find this when they need it.

On my current project, I'm changing the node author field based on the value of a user reference field on the node type: when a content admin sets the node reference field, the node author field is changed to match that user reference field value. Since the author field is shown in a fieldset, I wanted the summary on that fieldset to update when this change was made. It took me a while to figure out how, but it's pretty simple:

// Update the field summary if vertical tabs are in usevar tab = $('fieldset.node-form-author', context).data('verticalTab');if (tab) {  tab.updateSummary();}