Error Identification

Understanding WCAG2.0

If there are items that require mandatory items or values in a predetermined format to be entered, and if you do not want to accept the transmission unless it is entered correctly, display errors in an easy-to-understand way for the user. When displaying an error, for example, only changing the background color of mandatory items that are not entered is insufficient because the visually impaired person does not know the error (This does not mean that you should not change the color.Usability of sighted people improves by expressing colors.). It is necessary to explain the error with sentences.

It is good to check the error before sending using JavaScript.

Principle Understandable Information and the operation of user interface must be understandable.
Guideline Input Assistance Help users avoid and correct mistakes.
Criterion Error Identification
(3.3.1 A)
If an input error is detected automatically, the error location is identified and the error is explained in text to the user.

URL of Techniques for WCAG 2.0