In Javascript an object with a length property and a splice function is an array-like object. Chrome and Firebug display these like arrays:
a = {length: 1, splice: function(){}, 0:"some value"}
>> ["some value"]
$(".tagged span").slice(0,2) // on Stackoverflow
>> [<span class="item-multiplier">…</span>, <span class="item-multiplier-x">×</span>]
The arguments variable is a special case because it is an array-like object even though it does not have a splice function.