Input Validation and Error Indication
Many of the errors encountered during data input can be addressed via the use of masks. By using masks and other editor capaiblities - such as limiting input string length, specifying maximum and minimum allowed values, etc - you can control how users maniuplate data. But editors cannot solve all potential problems associated with data entry, since often, the values upon one another. In such instances, the XtraEditors provide you with flexible editor validation mechanisms. If validation fails, the editor doesn't allow focus movements and displays an error icon. End-users can point to that icon to see the error message. This takes place in the following cases:
- When moving focus away from the editor, if the entered value doesn't conform to the specified mask (the input hasn't been completed).
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When moving focus away from the editor, if an editor's Validating event handler specifies that the entered data is invalid.
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At any time, if you assign the error text directly to the editor's ErrorText property. This allows easy error indication when an editor's value validity depends on other controls.
The validation events allow multiple scenarios - changing the error message text, ignoring or resetting the value, etc. 
DXErrorProvider Component
The XtraEditors Library introduces a DXErrorProvider component, which is a more powerful and flexible version of the standard ErrorProvider component. With the standard component, you could only validate data in individual editors when they were about to lose input focus. DXErrorProvider offers you more flexibility by allowing you to validate the content of entire container controls - for instance, forms. And it has one more advantage - you can use up to six types of error notifications. There are three built-in types: error, warning and information message. You can also specify up to three custom notification types, i.e. supply your own icons to be displayed next to editors.
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