@, [, and ] in a URL query string for partial API call

I'm looking doing partial requests from the Google Picasa API. They show this as an exmaple:

GET https://开发者_如何学Cpicasaweb.google.com/data/feed/api/user/photosapi?kind=album&v=2.0&fields=entry(title,gphoto:numphotos,media:group(media:thumbnail),link[@rel='http://schemas.google.com/g/2005#feed'](@href))

I understand this has to be URL encoded before it's used, but how does the server interpret symbols like @, [, and ]?

Since this API call will be requesting an XML file, do these characters help the browser navigate the XML to get the requested information (since this is partial request of the album information, not a full dump of the user's photo data)?

I found the answer. This is the syntax for Google's Partial Response API calls.

More info here: http://code.google.com/labs/faq.html#experimental