How does php modify the xml element name?

How to modify the xml element name in php $ v = "abc ";
$ Note "-> item (0)-> getElementsByTagName (" name ")-> item (0)-> nodeName = $ v; // change the name to $ v, but the nodeName is read-only.
Is there any modification method, such as xml element attributes or values that can be modified, but the name cannot be modified?

Reply to discussion (solution)

Insert a new node to delete the old node.

But there are many byte points in the original label. how can I get the content and insert it into the new node?
Similar to JavaScript in html, you can obtain the content of all nodes.
Value = oldnode. innerHTML;
Newnode. innerHTML = value;
Is there any similar method?