如何在Nokogiri中的XML根节点之前添加注释？

Question

This is what I'm doing:

xml = Nokogiri::XML('<hello/>')
xml.root.add_previous_sibling(
  Nokogiri::XML::Comment.new(
    xml, '<!-- how are you? -->'
  )
)

This is what I'm trying to achieve:

<?xml version="1.0"?>
<!-- how are you? -->
<hello/>

I'm getting:

ArgumentError: A document may not have multiple root nodes.

What is the right way?

Answer 1

Comment should be added inside xml.children NodeSet.
Here is an example:

 xml = Nokogiri::XML('<hello/>')
=> #<Nokogiri::XML::Document:0x3fe1db8d0ed0 name="document" children=[#<Nokogiri::XML::Element:0x3fe1db8d0584 name="hello">]>

xml.children.before(Nokogiri::XML::Comment.new(xml, 'how are you?'))
=> #<Nokogiri::XML::Element:0x3fe1db8d0584 name="hello">

xml.to_s
=> "<?xml version=\"1.0\"?>\n<!--how are you?-->\n<hello/>\n"