The UserLand version of RSS 0.91 was the first direct ancestor of RSS 2.0. Every document in one of the predecessor formats of RSS 2.0 is a valid document of the formats with higher version numbers (with certain restrictions). All documents of the RSS versions 0.91, 0.92, and 0.93 are also valid RSS 2.0 documents. From version to version, new elements were added. In the process, more and more metadata was allowed
not only for a whole
channel, but also for individual elements of the
item type. The development of functionalities and language elements for aggregated feeds in the current syndication formats continues this tendency. In addition, restrictions such as on the maximum number of
item elements were lifted, ...