setValue
--------
- Should accept native type (eg. a .value of an identical type), 
- Should accept flexible string input
- Should accept |readable()|
- Should accept native type. Eg. Number for currency
- If validation fails then it should resolve to pre-existing value
- You should be able to set the value to null without throwing an error

readable
--------
- Returns string that can be interpreted by |setValue|
- If empty then should return an empty data type when passed to |setValue|

val
---
- Like 'readable' but returns a value representing data or null if not set
- Should be able to be interpreted by |setValue|

clear
-----
- Removes data, putting the type into a brand-new state