Tutorial :Add a dtd using nokogiri builder


I am using nokogiri to generate svg pictures. I would like to add the correct xml preamble and svg DTD declaration to get something like:

<?xml version="1.0" standalone="no"?>  <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">   <svg>  ...  

With builder I could use instruct! and declare! but I want to stick with nokogiri because I use it for other purpose in my project and I want to stay low on requirements. Do you have some ideas ?



You can now (don't know from which version) use Node#create_internal_subset to create the DTD node. For more info see: http://nokogiri.org/Nokogiri/XML/Builder.html

And scroll down to the "Document Types" section for an example.


Following is from a note at the bottom of the Nokogiri::XML::Builder page (maybe added recently), which I think will do the trick:

builder = Nokogiri::XML::Builder.new do |xml|    xml.doc.create_internal_subset(      'html',      "-//W3C//DTD HTML 4.01 Transitional//EN",      "http://www.w3.org/TR/html4/loose.dtd"    )    xml.root do      xml.foo    end  end    puts builder.to_xml  


Here is a possible solution, though it looks like a dirty trick:

#1. I build the svg document  builder = Nokogiri::XML::Builder.new do |xml|    xml.svg do      # ...    end  end    #2. I retrieve the svg root node  svg = builder.doc.xpath("/svg").first    #3. I define and parse an xml document with the required preamble and dtd  str =<<EOS  <?xml version="1.0" standalone="no"?>  <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1. /DTD/svg11.dtd">  EOS  doc = Nokogiri::XML::Document.parse(str)    #4. I add the svg node to the document above  doc.add_child(svg)  


For those working with HTML, Eric Walkers' example doesn't quite work since a doctype is automatically added. You need to remove it first:

builder = Nokogiri::HTML::Builder.new do |html|    html.doc.internal_subset.remove    html.doc.create_internal_subset('html', nil, nil)  end  

This will add the HTML5 doctype a.k.a. <!DOCTYPE html>


There does not appear to be any way to add a doctype using Nokogiri::XML::Builder. However, adding a doctype declaration to an XML document is of dubious utility, unless your tools require it. Read DTDs Don't Work on the Web by Henri Sivonen for some reasons why it's not a very good idea to use DTDs, and you should instead ensure your document is well-formed, and validate it against an external schema (which may be a DTD, or may be something more powerful like XSD or RELAX-NG) rather than a DTD embedded within the document.

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