Could do with more documentation for the `Formatter` class [procedures] in the `values` module

[amn]

Looks like the documentation strings for the methods of the Formatter class, have been written in somewhat inconsistent manner -- some of the procedures have doc. strings attached and some do not. There should be documentation for every part of the API, and per convention if the method is not private (i.e. with leading underscore in the name) and is part of a public construct, it should be documented and the documentation string is the canonical source of information for the method.