Used for data serialization logic and for field validation logic that is specific to a custom field type to convert the field value object into a validated, serialized string.
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
In a custom type-specific class, override the GetValidatedString method to define the following kinds of logic:
Data-validation, for example, to throw an exception in server-side code if the field is required.
Pre-update data processing, for example, to filter out bad data but not fail validation.
Serialization, for example, to convert a field value object into string format.