Hello, Ed,
The provided video is greatly appreciated. I was able to observe the same behavior on my end. Note that the IncludePrompt property is not relevant when the MaskType is Regex. However, I confirm it is not desired behavior to receive an exception when trying to set MaskType property at design time.
I have logged this on our feedback portal by making this thread public. You can track its progress, subscribe for status changes and add your comments on the following link - feedback item. I have also updated your Telerik Points.
Currently, you can set this property to RadMaskedEditBoxElement in the code behind:
this.radMaskedEditBoxElement1.MaskType = MaskType.Regex;
I hope this helps. Let me know if you have any other questions.
Regards,
Nadya
Progress Telerik
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