Example

try
{
  var node = document.getElementsByTagName('h1').item(0);
  var refnode = node.nextSibling;
  var newnode = document.createTextNode('That is why you fail.');
  node.insertBefore(newnode, refnode);
}
catch(err)
{
  alert(err.code);
}

The example above shows an insertBefore operation that will fail, because refnode is not a child of node. That operation produces a code 8 exception (NOT_FOUND_ERR).