title: What are the "response" and "request" arguments in jQuery UI Autocomplete's "source" callback?
body: <p>I'm looking at the autocomplete tutorial, and I have a few questions: <a href="http://jqueryui.com/demos/autocomplete/#option-disabled" rel="noreferrer">http://jqueryui.com/demos/autocomplete/#option-disabled</a></p>
  
  <pre><code>$( "#tags" )
              // don't navigate away from the field on tab when selecting an item
              .bind( "keydown", function( event ) {
                  if ( event.keyCode === $.ui.keyCode.TAB &amp;&amp;
                          $( this ).data( "autocomplete" ).menu.active ) {
                      event.preventDefault();
                  }
              })
              .autocomplete({
                  minLength: 0,
                  source: function( request, response ) {
                      // delegate back to autocomplete, but extract the last term
                      response( $.ui.autocomplete.filter(
                          availableTags, extractLast( request.term ) ) );
                  },
                  focus: function() {
                      // prevent value inserted on focus
                      return false;
                  },
                  select: function( event, ui ) {
                      var terms = split( this.value );
                      // remove the current input
                      terms.pop();
                      // add the selected item
                      terms.push( ui.item.value );
                      // add placeholder to get the comma-and-space at the end
                      terms.push( "" );
                      this.value = terms.join( ", " );
                      return false;
                  }
              });
  </code></pre>
  
  <p>So I understand the parameters for source is <code>request</code> and <code>response</code>. Are these reserved keywords? I couldn't find anything when typing this into google. I am unclear as to what is the request and response being passed into here. Is the request just grabbing the input? Where can I read up more on this?</p>