Template:MediaWiki URL rules
URLs must begin with a supported URI scheme.
https:// will be supported by all browsers; however,
news: may require a plug-in or an external application and should normally be avoided. IPv6 host-names are currently not supported.
If URLs in citation template parameters contain certain characters, then they will not display and link correctly. Those characters need to be percent-encoded. For example, a space must be replaced by
%20. To encode the URL, replace the following characters with:
Single apostrophes do not need to be encoded; however, unencoded multiples will be parsed as italic or bold markup. Single curly closing braces also do not need to be encoded; however, an unencoded pair will be parsed as the double closing braces for the template transclusion.