title: What does class ClassName < ::OtherClassName do in Ruby?
body: <p>Yesterday, I found the following code in <a href="https://github.com/dchelimsky/rspec/blob/ef449c38a7e98dd276ffb6e37758ef6f38a53801/lib/spec/runner/option_parser.rb#L6" rel="noreferrer">RSpec</a>:</p>
  
  <pre><code>class OptionParser &lt; ::OptionParser
  </code></pre>
  
  <p>What does this do? What is the difference between this and <code>class OptionParser &lt; NameSpace::OptionParser</code>?</p>