From The DoY Wiki
Only a small portion of HTML (also known as HyperText Markup Language) can be used on ShoutWiki sites. Because using HTML makes the markup more complex, it is usually recommended to use wikitext instead where possible.
Links (both internal and external) can only be created via the wikitext link syntax. The standard HTML code for links (
<a href="link target">Link title</a>) cannot be used.