title: What are the restrictions for method names in Ruby?
body: <p>For example, I found the method name <code>bundler?</code> in the following snippet, and don't know whether the <code>?</code> character is a specialized keyword or just part of the method name.</p>
  
  <pre><code># This is a predicate useful for the doc:guides task of applications.
  def bundler?
    # Note that rake sets the cwd to the one that contains the Rakefile
    # being executed.
    File.exists?('Gemfile')
  end
  </code></pre>