In my opinion, value 0 should have NotMasked variant, and value 1 should have Masked, which is also aligned with NVIC concept: set unmask then some function activate, set mask then some function deactivate.

Or even better, I suggest to use

 "MSK1": Alarm seconds mask
   ToMatch: [0, "Alarm set if the date/day match"] 
   NotCare: [1, "Seconds don’t care in Alarm comparison"] 

to make this values more clearly.

But this modification will break current api, so maybe we need more discussion on it?

and also, MSK1 ~ MSK4 share the same description, which is not correct, and need to be too.