Prototype adjacent() Method

Syntax:

element.adjacent([ selectors...]);

Return Value:

An array of HTML elements.

Example:

<html>
<head>
<title>Prototype examples</title>
<script type="text/javascript" 
   src="/javascript/prototype.js">
</script>
<script>

function listCities(){
   var arr = $('nyc').adjacent('li.us');

   arr.each(function(node){
      alert(node.nodeName + ': ' + node.innerHTML);
   });

}

</script>
</head>

<body>
   <ul id="cities">
    <li class="us" id="nyc">New York</li>
    <li class="uk" id="lon">London</li>
    <li class="us" id="chi">Chicago</li>
    <li class="jp" id="tok">Tokyo</li>
    <li class="us" id="la">Los Angeles</li>
    <li class="us" id="aus">Austin</li>
  </ul>

   <br />
   <input type="button" value="List Cities" 
             onclick="listCities();"/>
</body>
</html>

To understand it in better way you can Try it yourself.