C14N() on a node returns the root-node

[kripper]

Test case: https://onlinephp.io/c/f4d65

Given the following XML example, running C14N() on tag "NODE" returns the whole document (BUG). c14N() on tag "NODE" should only return the content of tag "NODE".

<?xml version="1.0"?>
<TEST>
  <NODE>
    here
  </NODE>
</TEST>