can you people guide me in this problem
when adding new patron and save patron 
currently if username is empty the username is saving firstname and surname in its field
my question is 
is it possible to replicate the cardnumber field value typed; into username field with prefix "CL" at the beginning
for example adding new patron in koha, i type 1234 in cardnumber and hit save button, can koha copy this 1234 into username with CL1234 automatically when the username field is empty