[YKWeyer]

Issue

Most of the DOIs imported by our editors do not respect the expected DOI format (starting with 10.), leading to incorrect URLs being generated in the frontend (the most common being https://dx.doi.org/https://doi.org/10. …, because editors save the entire URL in the DOI field).

Suggested changes

• Add a placeholder to the DOI input, showing the expected format
• Strip most common invalid prefixes when getting the DOI of a publication entry
• Generate a link to doi.org only when the returned DOI is matching the expected format (starting with 10.)
  • If it is not the case, then the value of the DOI will be outputted as text, as a fallback
• Minor improvement: use doi.org instead of dx.doi.org according to the DOI Resolution Documentation:

  The proxy service (both doi.org and the earlier but no longer preferred dx.doi.org) is accessible …

Resolves #93

[tinzog]

Thanks a lot for this PR, @YKWeyer! Wrong DOI values from editors pose a real problem .
We merged the PR into typo3-13 and added two follow-up commits:

• 4e3968f [BUGFIX] Fix DOI normalization and link generation without f:startsWith
• 7de22a2 [TEST] Add unit and functional tests for DOI handling

What changed:

• f:startsWith: This ViewHelper only exists since typo3fluid/fluid 4.5. Early TYPO3 13.4 releases ship an older Fluid version, so the citation list failed there. The check is now done in PHP: Publication::getDoiUrl() returns the resolver URL, or an empty string if the DOI is invalid. The partials only check {publication.doiUrl}.
• Cleanup: Cleaning, validation and URL building are now in a new DoiUtility. It also handles \url{…} including the braces, combined prefixes such as DOI: https://doi.org/…, www.doi.org and multi-line values.
• Validation: A value counts as a DOI only if it matches 10./, so text like "10. Auflage" is no longer linked.
• Encoding: Characters like #, ?, <, > and ; in the DOI are encoded in the link, so these DOIs open correctly at doi.org.
• Tests: We added unit tests for the utility and functional tests for both link block partials.

Thanks again for your contribution!