The API method is now in source, with a new name and more functionality. Details are:
Code:
def tb_category_visibility(self, category, operation):
'''
Hide or show categories in the tag browser. 'category' is the lookup key.
Operation can be:
- 'show' to show the category in the tag browser
- 'hide' to hide the category
- 'toggle' to invert its visibility
- 'is_visible' returns True if the category is currently visible, False otherwise
'''
I think you no longer need the variable hidden_categories.