title: Cucumber Capybara find checkbox by other than id, name, or label
body: <p>I'm trying to check a checkbox in my cucumber test, but I cannot figure out how to tell it to search by anything other than the id, name, or label.  I keep on getting this error:</p>
  
  <pre><code>cannot check field, no checkbox with id, name, or label 'xxxx' found
  </code></pre>
  
  <p>I have added an attribute of 'identifier' to each checkbox, with unique values, and would like to find the box by these terms.</p>