The Post formatter is called following the validation cycle. This formatter is responsible for applying pretty formatting for output values. Examples include masking a phone number or currency value w/ helpful formatting, such as "(555) 444-5555" (5554445555) or $3.50 (3.50)

The Pre formatter is called prior to the validation cycle. This formatter is responsible for preparing the visible value for validation. Common use-cases would include stripping special formatting provided by the post formatter for strings, or enforcing a specific value length or bound.