Every day we validate things from words in a sentence (to make sure they make sense) to change received from purchases. Thus, the concept is a natural and easy one for us to understand. Take the following phone number: 555-34567
Chances are, you quickly recognized the above phone number to be invalid. How? Your brain analyzed the phone number and noted that it contained eight numbers. After comparing this fact to the rule that defines valid local phone numbers as those that include seven numbers, your brain made a determination of true (the number was valid) or false (it was invalid). If you determine that the above number is valid, you can place the phone call. If, however, the number is invalid, your brain will log an error message something like "That number is wrong. I need to get the correct number and then try to call."
If we were to break down the validation process, it would look like the following:
In ActionScript, this process of analyzing information, comparing it to a set of rules, and then determining the data's validity is known as a validation routine. Just as your brain analyzes data instantaneously, an ActionScript validation routine takes just a split second to complete.
You usually need to validate data within a Flash application whenever you require the user to enter information into an input-text field for example, on forms (name, address, phone number, and so on), in passwords, on quizzes (to verify answers), and in e-commerce shopping carts (quantities, sizes, colors, and so on).