Your API will explode violently in IE < 8 || Quirks. This is because of gratuitous use of `setAttribute` along with `Array.prototype.slice.call` (dirty hack)[0]. IE < 8 || Quirks already treats HTML attributes and DOM properties identically[1], so really, DOM properties are preferred. More standards-compliant environments will reflect the property value in the corresponding attribute value (if possible).

Using `Object.prototype.toString.call` is also a pretty dirty hack, especially to detect an "array". I think `typeof obj === "object" && obj.length` would suffice, even if certain false positives like string objects leak through.

[0]: http://i.imgur.com/RNBYd.png

[1]: http://msdn.microsoft.com/en-us/library/dd347148(v=VS.85).as...