I understand concepts of JSON ok, but after starting to use ebay's api, I came across a notation which I've not seen before, and was wondering if anyone could explain what's going on with it?

{
"findItemsByKeywordsResponse": [
    {
        "ack": [
            "Success" 
        ],
        "version": [
            "1.5.0" 
        ],
        "timestamp": [
            "2010-06-16T08:42:21.468Z" 
        ],
        "searchResult": [
            {
                "@count": "0" 
            } 
        ],
        "paginationOutput": [
            {
                "pageNumber": [
                    "0" 
                ],
                "entriesPerPage": [
                    "10" 
                ],
                "totalPages": [
                    "0" 
                ],
                "totalEntries": [
                    "0" 
                ] 
            } 
        ] 
    } 
]

}

What's the "@count" thing? I noticed when I reference it in chrome, it throws an error:

But in Firefox not. JSON Lint reports it's valid, as I'd expect... ;)