insert_xml_into_nokogiri_document.rb

# The way to insert some xml into building xml with correct indents

builder = Nokogiri::XML::Builder.new(encoding: 'UTF-8') do |xml|
  xml.Batch do
    xml.Count 1
  end
end

batch_xml_element = builder.doc.at('Batch')
xml_text = '<Element><One>1</One><Two>2</Two></Element>'
xml_element = Nokogiri::XML(xml_text, &:noblanks).root 
batch_xml_element.add_child(xml_element)
builder.to_xml

# <?xml version="1.0" encoding="UTF-8"?>
# <Batch>
#   <Count>1</Count>
#   <Element>
#     <One>1</One>
#     <Two>2</Two>
#   </Element>
# </Batch>