Edit in JSFiddle

$(function() {
      var availableTags = [
      "Action Script",
      "Apple Script",
      "Asp",
      "BASIC",
      "C",
      "C++",
      "Clojure",
      "COBOL",
      "Cold Fusion",
      "Erlang",
      "Fortran",
      "Groovy",
      "Haskell",
      "Java",
      "Java Script",
      "Lisp",
      "Perl",
      "PHP",
      "Python",
      "Ruby",
      "Scala",
      "Scheme"
    ];
    function split( val ) {
      return val.split( /,\s*/ );
    }
    function extractLast( term ) {
      return split( term ).pop();
    }
 
    $( "#tags" )
      // don't navigate away from the field on tab when selecting an item
      .bind( "keydown", function( event ) {
        if ( event.keyCode === $.ui.keyCode.TAB &&
            $( this ).data( "ui-autocomplete" ).menu.active ) {
          event.preventDefault();
        }
      })
      .autocomplete({
        minLength: 1,
        source: function( request, response ) {
          //check if the request string starts with a space
          if(request.term===' ')
          {
            response([{value: "Enter Some text to search"}]);
            return false;
          }
          // 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;
        }
      });
  });

  <script src="//code.jquery.com/jquery-1.10.2.js"></script>
  <script src="//code.jquery.com/ui/1.10.4/jquery-ui.js"></script>
 <div class="ui-widget">
  <label for="tags">Tag programming languages: </label>
    <input id="tags" size="50"></input>
</div>

<div style="height:2px; background-color:gray; margin-top:100px;"></div>
  <iframe id="iframe1" src="http://jqfaq.com/AdPage.html" style="width:100%;border:none;" />