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If you have a DOI, use that alone, starting with the prefix: 10.XXXX. The DOI is preferable because it will continue to function if the URL becomes non-functional.

You don’t need to worry about the following fields: URN, First RILM Access, Last Verified, Requires Payment, or Requires Registration.

But you may occasionally want to use Supplemental. Check this box if the URL or DOI you entered is for a personal website, supplemental material posted on a journal or institutional website, or online resource cited in the abstract.