Morpho

The Morpho XML editor allows the copying and pasting of tree nodes (and their
children). Currently, copying the root node does not work, however. This would
be very useful, however, in cases like eml-attribute documents where there are
many attribte nodes directly under the root and one wishes to copy all of them
to a new document.

A simple replacement of the root node with a new root is easily implementsed.
The problem is that this approach also copies identifier nodes. We thus need to
put the old identifier back into the new identifier nodes.