Nokogiri conundrum

code.rb

  def to_ddoc
    xmldata = Nokogiri::XML(ddoc_container)
    xmldata.css('DataFile').each_with_index do |el, i|
      frag = Nokogiri::XML.fragment(documents[i].datafile(i))
      el.replace frag
    end
    xmldata.to_xml
  end

sample.ddoc.xml

<?xml version="1.0" encoding="UTF-8"?>
<SignedDoc format="DIGIDOC-XML" version="1.3" xmlns="http://www.sk.ee/DigiDoc/v1.3.0#">
  <!-- Default namespace exists in Nokogiri::XML object, but it's missing in serialized form -->
  <DataFile ContentType="EMBEDDED_BASE64" Filename="10.1.1.210.2072.pdf" Id="D0" MimeType="application/pdf" Size="684191">
    <!-- BASE64 data truncated -->
  </DataFile>
  <!-- Extra metadata here -->
</SignedDoc>

xmldata_debug_fragment

# This is xmldata in pry before to_xml call
=> #(Document:0x3fdeceebf89c {
  name = "document",
  children = [
    #(Element:0x3fdeceebf7c0 {
      name = "SignedDoc",
      namespace = #(Namespace:0x3fdeceebf798 {
        href = "http://www.sk.ee/DigiDoc/v1.3.0#"
        }),
      attributes = [
        #(Attr:0x3fdece969fb4 { name = "format", value = "DIGIDOC-XML" }),
        #(Attr:0x3fdece969fa0 { name = "version", value = "1.3" })],
      children = [
        #(Text "\n"),
        #(Element:0x3fdecf67ab04 {
          name = "DataFile",
          namespace = #(Namespace:0x3fded0e98a60 {
            href = "http://www.sk.ee/DigiDoc/v1.3.0#"
            }),
          attributes = [
            #(Attr:0x3fded0e989e8 {
              name = "ContentType",
              value = "EMBEDDED_BASE64"
              }),
            #(Attr:0x3fded0e989c0 {
              name = "Filename",
              value = "10.1.1.210.2072.pdf"
              }),
            #(Attr:0x3fded0e989ac { name = "Id", value = "D0" }),
            #(Attr:0x3fded0e98998 {
              name = "MimeType",
              value = "application/pdf"
              }),
            #(Attr:0x3fded0e98984 { name = "Size", value = "684191" })],
          children = [
            #(Text "JVBERi0xLjQKJdDUxdgKNiAwIG9iaiA8PAovTGVuZ3RoIDQ2NTIgICAgICAKL0Zp\nbH
          }),