Message
ext-link with @ext-link-type="doi" must contain a correctly formatted DOI in the @xlink:href
attribute "@xlink:href" and/or text "."
Rule XPath:
This rule ASSERTS the following, raising an alert if FALSE:
not(@ext-link-type = 'doi')
or (@ext-link-type = 'doi'
and matches(replace((@xlink:href, text())[1], '\p{Z}', ' '), '^(https?://(dx\.)?doi.org/)?10(\.\d+)*/[^\s]+$')
)