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First thing's first; I found that only Google will validate extended sitemaps. Yahoo/Bing states in SE/WMT that they will parse the valid information in the sitemap regardless, but I'm not perfectly clear on this. You can search within sitemap category on the search engine pages. Remember now that the src attribute is not a link, so if this is how you are adding multimedia to your pages, I'm not sure how you will include them in your sitemap. There are many discussions about iframes passing page rank, and the consensus is that they currently do not. If this is the way it has to be for this project, then of course you should add alternate text for iframe and frameset elements, add a title, and maybe include a link inside the iframe. Really, what else can you do? But some good news can be found here http://www.stonetemple.com/articles/interview-matt-cutts-012510.shtml. It's possible Google may change the way pageRank flows through these kinds of links.