empty link Tags: <a href="[url]" title="[title]">[nothing here]</a>
nested link tags <a href="[url]" title="[title]"><a[missing params]>[text here]</a></a>
missing link params: <a[missing params]>[text here]</a>,
wrong positioning of the tag: [text here]<a href="[url]" title="[title]">[nothing here]</a>,
plain text url: <a href="[url]" title="[title]">[nothing here]</a>[url again] and
split-up tags: <a href="[url]">[first part of the link text]</a><a href="[url]">[second part of the link text]</a><a href="[url]">[third part of the link text]</a>