title: Boolean for API Get request, with default. Y/N/All or true/false/all
body: <p>I'm implementing a filter for a boolean value, but I want to have a default value, so for example. </p>
  
  <pre><code>parameter omitted - returns where isPublished=true
  isPublished=true - return's where isPublished=true
  isPublished=false - return's where isPublished=false
  </code></pre>
  
  <p>What If I want to return everything? I could do isPublished=all but some have complained that this is confusing as its not then a true boolean. </p>
  
  <p>I could also go with Y/N/All or Either or Both</p>
  
  <p>What are others views? </p>