In this answer the author used the following syntax to link to external pages:
Most commonly are the rules from [Duden][1] or from ["Rat für deutsche Rechtschreibung"][2] quoted. [1]: http://www.duden.de/sprachwissen/rechtschreibregeln [2]: http://rechtschreibrat.ids-mannheim.de/download/regeln2006.pdf
The links are displayed as HTML/URL instead of being clickable.
Most commonly are the rules from http://www.duden.de/sprachwissen/rechtschreibregeln">Duden or from http://rechtschreibrat.ids-mannheim.de/download/regeln2006.pdf">"Rat für deutsche Rechtschreibung" quoted.
However, when editing this answer, it's correctly displayed in the preview.