code: function tag(fn, uid) {
  		// Overwrite the uid with the custom one.
  		if (uid) { fn.uid = uid }
  		// Or generate a new one if needed.
  		else if (!fn.uid) { fn.uid = nextUid++ }
  		return fn.uid;
  	}
docs: Utilities and shims ------------------- /*
  Returns a unique id distinguishing the function. The same
  function will always return the same id. Functions will be
  tagged with a custom uid if provided as argument.
  
  Internally, this attaches a `uid` property to the function.