Nokogiri copy node between documents and DOMException WRONG_DOCUMENT_ERR

copy_node_btw_docs

require 'nokogiri'

# The following illustrates unexpected behavior of the Nokogiri::XML::Document.add_child method.
# When called from a new document, the behavior is different depending on if the argument
#  is a newly created node or duplicate node.

# String of XML for Nokogiri to parse.
dummy_xml = '<?xml version="1.0" encoding="UTF-8"?>
<root>
    <Dummy>Text1</Dummy>
    <Dummy>Text2</Dummy>
    <Dummy>Text3</Dummy>
</root>'

# Existing document from which to copy a node.
x_doc = Nokogiri::XML::Document.parse( dummy_xml )

# New document into which the copied node will go.
n_doc = Nokogiri::XML::Document.new

# Duplicate the node to copy to new document.
duplicate = x_doc.xpath("/root/Dummy[2]").first.dup

# Fresh node created for new document.
fresh = Nokogiri::XML::Node.new( "freshNode", n_doc )

# Using add_child method of new document with duplicate will fail.
begin
  n_doc.add_child( duplicate )
rescue RuntimeError => run_err
  puts run_err.to_s
end

# Using add_child of new document with freshly created node will work.
# Using add_child of freshly created node with duplicate node will work.
begin
  n_doc.add_child( fresh )
  n_doc.root.add_child( duplicate )
rescue RuntimeError => run_err
  puts run_err.to_s
end

# Print document.
puts "Document with fresh node:"
puts n_doc

# For contrast, using root= of newly created document with duplicate node will work.

# New document into which the copied node will go.
n_doc = Nokogiri::XML::Document.new

# Setting the duplicate node as root will work.
begin
  n_doc.root=duplicate
rescue RuntimeError => run_err
  puts run_err.to_s
end

puts "Document with duplicate node:"
# Print document
puts n_doc