IE 9 Type Mismatch with importNode

parent.appendChild(parent.ownerDocument.importNode(node, children));

Yes. DOM Level 1 decided that ownerDocument is set at the time the node is created, and never reset thereafter.

Different DOMs may implement Nodes in completely different ways, and the implementation details may not be compatable even though both support the same public APIs. This can be true even within a single DOM implementation, since it may decide to use different kinds of Node in order to provide special behaviors for particular kinds of documents (perhaps guided by DTD/Schema or Namespace information). Thus, attempting to move a Node from one Document to another would be non-portable at best, and the DOM throws a DOMException (WRONG_DOCUMENT_ERR) when you attempt to do so. Exposing ownerDocument introduced no additional constraints... and added significant value, e.g. by allowing you to write myNode.appendChild(myNode.getOwnerDocument().createTextNode("new child")); even when myNode is not currently part of the Document's main tree.

The clone will be owned by the same Document as the node it was cloned from.

The DOM Recommendation specifies that appendChild Mustthrow DOMException (WRONG_DOCUMENT_ERR) if an attempt is made to insert a node from one ownerDocument into a tree with a different ownerDocument. Some DOM implementations may allow this code fragment to work in specific circumstances, when they know that the underlying representation of the nodes is compatable, but that is considered non-compliant behavior.

DOM Level 2 defines an importNode() method that performs this operation. It is up to the implementation to do this in a standard way that works across implementations or in a more efficient way that uses knowledge of that implementation's data structures. If you're working with a Level 1 DOM, you have to copy the content manually.

DOM Level 3 defines an adoptNode() method that performs this operation.