Unable to use send_key() for a iframe. How to select this iframe and which element inside this should be use for send_key()?

and iframe html code
<iframe class="textarea" src="/framework/html/blank.html" style="width: 99%; border-width: 1px; height: 332px;">
#document
<html webdriver="true">
<head>
</head>
<body> … </body>
</html>
</iframe>
How to send the value to description?
One more thing i want to know that this code of frame is not coming when i go for "view page source " in browser?