Good Question 🙂
I can not exactly help you with documentation – but I can give a little background on how it works .
wordpress uses a jQuery script called password-strength-meter.js (found in the wp-admin/js) directory .
It is actually only a function (called passwordStrength(f,i,d) where f = password1, i = user_login and d = password2. ) that returns the “stregth” (or mismatch) as integer. to call and use that function, you need a second javascript (for example – user-profile.js found in the same directory – but also specific to the edit-profile page)
In shorts – you can copy the password-strength-meter.js and use it as a “jQuery plugin” of sorts – but IMHO – you will need to write another javascript to use it – depending on what exactly you want to achieve – how , and also where .
(you can take the user-profile.js as reference , copy and modify for your needs)
If no one else gives you a better answer (and I hope someone will) It might be the case to just use some other Jquery password strength plugin that is maybe easier to implement and better documented.
If you choose that option – You can find a list here :
you can also find a simple nice tutorial here that might let you better understand the process:
http://net.tutsplus.com/tutorials/javascript-ajax/build-a-simple-password-strength-checker/