OPML is an plain-xml-based file format for representing hierarchical outlines, and is used most commonly for allowing transfer of lists of RSS subscriptions from a feed reader or from a podcast consuming client.
OPML was created by UserLand Software to store and share outlines, hierarchical text documents where child data could be hidden or expanded.
Subscription list / podcast list
Software that supports OPML export:
- iTunes — SuperUser question
- to be expanded
OPML uses RFC 822 dates. The spec notes:
- All date-times conform to the Date and Time Specification of RFC 822, with the exception that the year may be expressed with two characters or four characters (four preferred).
RFC 822 dates are less than ideal compared to ISO 8601.