Returns a list of all categories, not just main categories .
Not all categories have a parent category. Internal categories will usually have a parent category. If a category has no parent category, this value will not be returned at all.
Three category types: main categories, tags, and internal categories (e.g., departments, groups). Internal categories are used when a department wants to contribute to its group of events.
XML is returned by default, but the format can be specified explicitly in the URL.
All three categories
An internal category with a parent category
Example with different category types and a parent category
This API is similar to Categories API. It is a new API that includes values not included in Categories API. This API exists to get all categories, because Categories API previously returned all categories, but now it returns only main categories.