How to update a data card field value from an action

So after some testing, I found that you have to set the data card value to a context value. But you have to be careful because the context value should be set when the form is visible from the source or else you run the risk of accidentally setting bad data. So basically it goes like this:
- set Data Card Value default property to a contextValue
- Set the contextValue to the source of that field on screen visible
- in your button call UpdateContext and set the contextValue to whatever you want

This sets the value. I'll be blogging it with a bit more information shortly. Stay tuned.