Question about the RegExp type and how it's used.

[mypark]

I'm a bit confused about the RegExp type shown in the readme. Normally you would want to test a field against a RegExp pattern, e.g. check for a valid email, rather than check that a field is a RegExp pattern (as shown in the example). Would you have to create a refinement for the former use case of checking a field against a pattern? Why would you want a RegExp type in tcomb otherwise? What would it be used for?