Defines semantics for standard casting mechanisms to be called after a given value has been parsed from a document. The current out of the box casters include:

• :noop <-- the default
• :string
• :float
• :integer
• :atom
• :existing_atom
• :boolean
  • If the input is a string, the conversion will consider ["1", "on", "true", "yes", "y", "t"] as truthy values and all other values as falsy
  • If the input is not a string, the conversion will force a boolean value by calling !! on the provided value

If the above casters do not cover a particular case (for example, Date parsing) then a function can be provided instead to resolve the correct value.