This function inserts a new node right before the reference node.
If you plan to do further modifications on the appended child you must use
the returned node.
Parameters
newnode
The new node.
refnode
The reference node. If not supplied, newnode is
appended to the children.
Return Values
The inserted node.
Exceptions
DOM_NO_MODIFICATION_ALLOWED_ERR
Raised if this node is readonly or if the previous parent of the node
being inserted is readonly.
DOM_HIERARCHY_REQUEST_ERR
Raised if this node is of a type that does not allow children of the
type of the newnode node, or if the node to
append is one of this node's ancestors or this node itself.
DOM_WRONG_DOCUMENT_ERR
Raised if newnode was created from a different
document than the one that created this node.