How to use a colon (":") in a Nokogiri node name

As I see it, you have three options:

You're using namespaces

Then you can declare the namespace and use the xml[] method:
```
builder = Nokogiri::XML::Builder.new do |xml|
  xml.root('xmlns:node' => 'http://example.com') do
    xml['node'].name
  end
end
```
Output:
```
<root xmlns:node="http://example.com">
  <node:name/>
</root>
```
This method is a bit trickier if you want to add a namespace onto the root element though. See "How to create an XML document with a namespaced root element with Nokogiri Builder".
You're not using namespaces but want/need an element name with a colon:

In this case, you need to send the method named "node:name" to the xml block parameter. You can do this with the normal ruby send method:
```
builder = Nokogiri::XML::Builder.new do |xml|
  xml.root do
    xml.send 'node:name'
  end
end
```
this outputs:
```
<?xml version="1.0"?>
<root>
  <node:name/>
</root>
```
You're not sure what this “namespace” business is all about:

In this case you're probably best avoiding using colons in your element names.

An alternative could be to use - instead. If you did this you'd need to use method 2. above, but with xml.send 'node-name'. I include this option because you don't mention namespaces in your question, and colons are used in them (as method 1. shows) so you're safer not using colons to avoid any future problems.

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