These standalone characters often indicate issues with encoding or
copy/paste in languages with accents like French and Spanish. For
example: foreˆt should be forêt.
It is not possible to fix these issues automatically, but this will
print a warning so you can notify the owner of the data.
I'm only concerned with validating issue dates here. In DSpace they
are generally always YYYY, YYY-MM, or YYYY-MM-DD (though in theory
they could be any valid ISO8601 format).
This also checks for cases where the date is missing and where the
metadata has specified multiple dates like "1990||1991", as this is
valid, but there is no practical value for it in our system.