This is just a guess, but perhaps something like: <a href="http:&#x2F;&#x2F;www.chiark.greenend.org.uk&#x2F;~sgtatham&#x2F;coroutines.html" rel="nofollow">http:&#x2F;&#x2F;www.chiark.greenend.org.uk&#x2F;~sgtatham&#x2F;coroutines.html</a>