The "apple_categories.txt" file contains a list of the current Apple podcast categories, which are mostly the industry standard.
The "categories.txt" file contains a deduplicated set of those categories, that could be used as a flat list of labels.
Using labels, a political history podcast could declare its categories as:
- Politics
- Government
- History
- Learning
- Education
Any number of categories could be added as a flat list instead of heirarchical category sets.
It would be fairly trivial to take the compound categories like "Health & Fitness" when discovered in a feed, and convert those into their single label equivalence.