Selecting an element in iframe with jQuery

In our application, we parse a web page and load it into another page in an iframe. All the elements in that loaded page have their token IDs. I need to select the elements by those token IDs. Means - I click on an element on the main page and select corresponding element in the page in the iframe. With the help of jQuery I'm doing it in the following way:

function selectElement(token) {
     $('[tokenid=' + token + ']').addClass('border'); 
}

However with this function I can select the elements in the current page only, not in the iFrame. Could anybody tell me how can I select the elements in the loaded iFrame?

Thanks.