Message
related-article must have attributes ext-link-type="doi" and xlink:href containing a DOI, or have attributes ext-link-type="uri" and xlink:href containing a URI that starts with http or https and is not a DOI URL.
Rule XPath:
This rule ASSERTS the following, raising an alert if FALSE:
(@ext-link-type = 'doi' and matches(@xlink:href, '^(https?://(dx\.)?doi\.org/)?10(\.\d+)*/[^\s]+$'))
or (@ext-link-type = 'uri' and matches(@xlink:href, '^https?://[^\s]+', 'i') and not(matches(@xlink:href,
'^(https?://(dx\.)?doi\.org/)', 'i')))