number Field Type - explanation for "grouping" option missing

[Burgov]

As stated in the title: there is no explanation for the "grouping" option for number field type.

[weaverryan]

This particular options was originally omitted because I couldn't easily determine what it does. It's used inside NumberToLocalizedStringTransformer to setup a NumberFormatter instance. However, due to the poor documentation on the GROUPING_USED attribute, I'm not sure what the end result of this is.

If someone can shed light on the NumberFormatter::GROUPING_USED attribute, it should be easy to fill in this missing documentation.