Message
Missing namespace for foo
Explanation
This element is in a namespace, but you have not declared the namespace.
Solution
Declare the namespace at the top of your feed. For example, if you use dc:date in your feed, you will need to declare the proper dc namespace, like this:
<rss version="2.0" xmlns:dc="http://purl.org/dc/elements/1.1/">
Check the full list of namespaces for the exact declaration you need.
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