Check and run a test on each character in text box without hitting any button

Any feedback on how to check for uppercase. lowercase etc as user inputs password into text box? For example as soon as user types "a" we should know its a lowercase letter, and display confirmation of such occurrence  before user presses the "enter" button.

Need to figure out how to do this with App Inventor 2. 

Used the trace function in Python as in:

 aName.trace("w", myfunc)

You will notice this on this website:

http://www.passwordmeter.com/

the "score" label changes as you type the password with each character.

The only way to do it is with a timer...  Enable it when the textbox receives focus... then, just work through each character...  The textboxes have no formatting capabilities...

Thanks Enis! I'll give it a try......