In the patterns.txt file is a list of regex patterns for common private and member-only podcast feed urls. This list is meant for publishers of those feeds to be able to list their patterns so that public directories and aggregators can test against them when accepting new feeds for listing. Anything in this list should be regarded as a private or membership based feed which should not show up in public listings.
Detecting private feeds by url is difficult. Publishers are encouraged to submit pull requests to this list to make it easier for the open podcast industry to avoid listing feeds publicly that it should not.