suppose i had an rss feed for a wordpress blog, and i wanted to include the id's of the site and post in the <item> for each post. is there any standard way to do this? if not, is there a namespace defined for wordpress blogs that might provide some prior art?

There is no standard way to include site and post IDs in the <item> elements of an RSS feed for WordPress blogs. However, the Jetpack plugin for WordPress provides a way to add custom namespaces and elements to the RSS feed, which could be used to include site and post IDs. The Jetpack plugin issue #996 discusses adding a <site> element with a custom namespace to include the site ID, and a <post-id> element to include the post ID. The proposed namespace was:
<site xmlns="com-wordpress:feed-additions:1">1234</site> <post-id xmlns="com-wordpress:feed-additions:1">5678</post-id>
This namespace was just a suggestion, and it was recommended to use a more appropriate namespace prefix. For example:
xmlns:wp="" <wp:site>1234</wp:site> <wp:post-id>5678</wp:post-id>
While this approach was discussed, it does not seem to have been implemented in Jetpack or WordPress core. However, it provides a potential solution and prior art for adding custom elements to the RSS feed for including site and post IDs. If you need to include site and post IDs in your WordPress RSS feed, you could implement a similar approach by adding a custom filter to the 'rss2_ns' and 'rss2_item' hooks in your theme's functions.php file or a custom plugin.
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