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What is the best way to handle content that is on multiple pages? Should I link just to the first page or have a link to every page?
Please note that the priority you assign to a page is not likely to influence the position of your URLs in a search engine's result pages. Search engines may use this information when selecting between URLs on the same site, so you can use this tag to increase the likelihood that your most important pages are present in a search index
I was hoping Google had one saying if they require any of the "optional" attributes.
You can create a Sitemap based on the Sitemap protocol, or you can submit a text file or RSS/Atom feed as a Sitemap.
Google adheres to Sitemap Protocol 0.9 as defined by sitemaps.org. Sitemaps created for Google using Sitemap Protocol 0.9 are therefore compatible with other search engines that adopt the standards of sitemaps.org.
FWIW: I only use a URL and priority in mine and don't have any errors or issues with them, but setting a lastmod and chanfreg lowered the frequency of the crawling of the URLs they were set for.