Validating numeric input
Custom validation needs to notify users in an accessible way as described in the User Notifications part of this tutorial.Client-side validation alone does not ensure security; therefore data needs to be validated on the server-side as well.Instead, it will display a message that is generated by the web browser itself.Note that the label also displays “(required)”, to inform users that don’t use assistive technology or use older web browsers that do not support the HTML5 attribute informs assistive technologies about required controls so that they are appropriately announced to the users (as opposed to validating the input).Depending on browser support, the url field can be automatically validated when submitted.
So checking what users write in your app fields is very important aspect to build a robust and secure apps.
Most often, the purpose of data validation is to ensure correct user input.
Validation can be defined by many different methods, and deployed in many different ways.
HTML5 defines a range of built-in functionality to validate common types of input, such as email addresses and dates.
In some situations, such as validating custom controls or supporting legacy browsers, additional scripting may be necessary to validate user input.
If the email address is not in the standard format (containing "@" and "."), the validation fails, an Error Provider icon is displayed, and the event is canceled. Active Control property to the current form, focus events occur in the following order: Caution Do not attempt to set focus from within the Enter, Got Focus, Leave, Lost Focus, Validating, or Validated event handlers.