Message
Identifier “foo” is not in canonical form (the canonical form would be “bar”)
Explanation
URIs used as identifiers should be in canonical form, as described by section 6 of RFC 3986. This means that insignificant differences (e.g., case of hostname) are removed, so URIs can be compared character-by-character to determine equivalence. This is particularly important when content is syndicated, and the same entry may appear in multiple feeds.
Also avoid leading and trailing whitespace as clients vary in their interpretation of such characters.
Solution
All newly issued ids should be in canonical form. Use the canonical form given in the warning message for guidance.
Notes:
- Do not update previously issued ids, unless they were issued in error.
- Do not canonicalize ids that you are resyndicating from other sources. Those must be character by character identical to the original. Instead, consider contacting the original source and see if this can be corrected for any new ids they may issue.
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