Sometimes it is necessary to create a custom function that allows implementing your own logic for filtering data in an auto filter row.
To create this function, it is necessary to implement the ICustomFunctionOperator interface. Finally, to register a custom function, call the CriteriaOperator.RegisterCustomFunction method with your custom function instance at the application startup.
This example illustrates how to add a custom function that will determine whether or not numbers in a cell are contained within the filter range.
See also:
How to create a custom ASPxGridView's filter insensitive to the number of spaces and punctuation
How to register a custom filter function and use it in GridControl