Format time to show year only in choropleth time slider

[TenThumbsWPG]

There may already be a way to do this, but I was not able to stumble on it...

I would like to be able to control the data format in the slider bar in a time slider choropleth. In my case (and I believe many others), I am describing annual trends and all that is required in the slider is the year.

I am requesting:

1. Ability to set the time format displayed in the choropleth time slider itself by passing a date format. or setting a "show year only" variable, or if this is already present,
2. Enhanced documentation describing how this can be modified.