execcommand erase link

There is param unlink: http://msdn.microsoft.com/en-us/library/ms537431%28v=VS.85%29.aspx

Now, I want to use same button for make link and erase it.
Erase it in case that under selection there is a link.

If I check slection with selectionRange or cross browser compatible things I get only url text, which does not tel me there is a link.

Any suggestion, how to chech that user selected text that is actualy a link. ?