How to prevent Nokogiri from adding <DOCTYPE> tags?
The problem occurs because you're using the wrong method in Nokogiri to parse your content.
require 'nokogiri'doc = Nokogiri::HTML('<p>foobar</p>')puts doc.to_html# >> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd"># >> <html><body><p>foobar</p></body></html>Rather than using HTML which results in a complete document, use HTML.fragment, which tells Nokogiri you only want the fragment parsed:
doc = Nokogiri::HTML.fragment('<p>foobar</p>')puts doc.to_html# >> <p>foobar</p>
The to_s method on a Nokogiri::HTML::Document outputs a valid HTML page, complete with its required elements. This is not necessarily what was passed in to the parser.
If you want to output less than a complete document, you use methods such as inner_html, inner_text, etc., on a node.
Edit: if you are not expecting to parse a complete, well-formed XML document as input, then theTinMan's answer is best.