What is a regular expression that accepts only characters ranging from a to z?
Try to use this plugin for masking input...you can also check out the demo and use this plugin if this is what you may want...
Masked Input Plugin
As you can see in the demonstration that you can use both alphatbets and numbers in a combination for complex textbox validations where an user might want to type not only alphatbets(azAZ) but also with numbers too(ie. alphanumberics)...specific validations like accepting only numbers in particular format(eg.phone numbers) can be done...that is the case when you can use this plugin for different circumstances..
hope this helps...