The validation of user data in forms is usually reported in an only binary valid/invalid result. If there is an error in the input values only this fact is reported and in best case an example of how a correct value should look like is shown (see Figure 1, "Conventional validation").

Figure 1, Conventional validation

From the user's perspective it would be more helpful if there is a more detailed feedback on the errors. How this might look like is shown in Figure 2, "Detailed feedback". If the input is not correct it is first displayed, as usual, that an error occured ([a]). If it is not clear to the user why the input he made is rejected, he can hover the cursor over the input field and additional selection fields will be shown (the colored boxes in [b]). If the user moves the cursor over these, a detailed message explains what exactly is wrong with the input ([c] to [e]).

Figure 2, Detailed feedback

The disadvantages of this method of validation are the more complex implementation (the validation can not be done by a single regular expression) and the slower validation process in case of an error: the process is not terminated upon the first occurence of an error, but the input values are checked to their end of further errors.