Validating against a Moose type-constraint without setting field

[sundialsvc4]

(Pardon me ... I am having a Senior Moment™ ...)

I need to validate a value against the type-constraint associated with a particular Moose has field, without actually setting the field’s value.   That is to say, given the field name and a variable containing a value that I want to check, I want to fire the field’s validation-constraint if it has one, and see if the value that I am presenting is agreeable to it.   (I had written notes that Moose’s “Recipe #4” told how to do that, but I can’t find that example now.   So, heck, thought I’d just ask...)

Thanks in advance.   (Now, where in the heck did I put my glasses?   Durn things are, uhh, “obviously broken” anyway ...)