RSS 2.0 introduces namespaced modules to the simple strand of RSS. The specification document states:
A RSS feed may contain elements not described on this page, only if those elements are defined in a namespace. The elements defined in this document are not themselves members of a namespace, so that RSS 2.0 can remain compatible with previous versions in the following sense ? a version 0.91 or 0.92 file is also a valid 2.0 file. If the elements of RSS 2.0 were in a namespace, this constraint would break, a version 0.9x file would not be a valid 2.0 file.
Other than not defining a namespace for the core elements of RSS 2.0, the modules work in the same way as the modules for RSS 1.0: declare the module's namespace in the root element (which in the case of RSS 2.0 is, of course, rss) and then use the module elements as directed by their specification. Parsers that do not recognize the namespace just ignore the new elements.
Whether or not RSS 1.0 modules can be reused within RSS 2.0 is currently a matter of debate. To do so requires the feed author to declare two additional namespaces within the root element: the namespace of the module and the namespace of RDF. Some people find this additional complexity distasteful, and others find the rejection of the additionally powerful metadata a great shame. Still others, however, are using modules that declare the rdf:resource attribute without flinching.
While this argument rages (I advise you to check out the relevant email lists for the latest blows and parries), we can always bear in mind the simple way to convert between the default module styles, which we will consider now.
RSS 1.0 modules, you will remember, declare everything in terms of RDF resources. This is done with the rdf:resource attribute. For example, a fictional element pet:image, used to denote an image of the feed author's pet, would be written:
whereas in RSS 2.0, the default lack of RDF means you must just declare the URI of the image as a literal string:
But the differences go deeper than this, as we will now see as we design a new module: mod_Book.