Good question: I've started with `*` but got the following error:
```
2013-07-17 11:20:39,675 build/ol.js: java -jar build/plovr-eba786b34df9.jar build buildcfg/ol.json
JSC_TYPE_MISMATCH. actual parameter 1 of ol.Collection.prototype.forEach does not match formal parameter
found   : function ((null|ol.control.Control)): undefined
required: function (*, number, (Array|null)): ? at ../src/ol/map.js line 333 : 6
```
from: https://developers.google.com/closure/compiler/docs/js-for-compiler:
`*`: Indicates that the variable can take on any type.
`?`: Same as `*` and the compiler should not type-check any uses of it.