Users should be able to allow properties with datatype "String" to link to external websites like external identifiers by adding a property for a formatter URL that is linked to the wikidata formatter URL property.

Only external identifiers are currently able to have formatter URLs to link off the wikibase, this behavior is unlike wikidata (https://www.wikidata.org/wiki/Property:P1793). Some properties of things aren't external identifiers but could be useful to link to a different website, such as linking regular expressions to a site where you can test it and see how it works.