Add to this category registry a new category having the specified categoryName, possibly changed by the registered category name filter callback, and default threshold levels if (the possibly filtered) categoryName is not present in the registry and the number of categories in the registry is less than the registry capacity. Return the address of the (possibly newly‐created) non‐modifiable category having (the possibly filtered) categoryName, if such a category exists, and the address of the non‐modifiable Default Category otherwise. The behavior is undefined unless categoryName is null‐terminated. Note that a valid category address is always returned.