> Basic example: If you want to mix data from several formats in one document. Can you get more concrete on why you would want to mix formats? So far what I ha

> Basic example: If you want to mix data from several formats in one document. Can you get more concrete on why you would want to mix formats? So far what I have seen namespaces were used just to extend one format. > Now let's say both the RSS-feed and the custom-data contains both a "link" element and a "title" element. Easily avoided if you just extend one format, but can happen if you would want to mix existing formats because of some reason. > - How can a RSS-library validate that the feed format itself is correct? You still need some code that parses the non-RSS part anyway, which can validate it. Don't you usually have just one parser that parses RSS and the non-RSS at the same time? If not, how are you passing your non-RSS XML tree-parts from the RSS-only library to the "new stuff"?