Filter Categories in meta box for CPTs
Working with a custom post type in WordPress, I would like to use the categories. So I added the categories to the cpt. No problems here.
But, when adding or editing cpt items, I would like to filter the categories they can choose from.
Currently it shows all categories. But I want to show only specific categories (or categories below a specific parent category).
FYI: A special taxonomy for the cpt is not an option in my use case.
I cannot find a filter / action I could use to filter all categories shown on a edit page for a specific CPT.
Example of the situation
A custom-post-type named ‘Books’. Normal WordPress categories: ‘category A’, ‘category B’, ‘subcategory A-1’, ‘subcategory A-2’
When editing a ‘Book’, I want the category select box to show: ‘subcategory A-1’, ‘subcategory A-2’. And omit all other categories.
All help is appreciated.