C# Masked TextBox Winform

I have a Masked TextBox in a Winform, it is currently set to phone number. I need it to accept letters also (125E4-GF215) 5 letters or Character then a dash then 5 Character like this format. I have read about Regular expression but have seen no examples on how to implement it.

Any help would be thankful.

https://docs.microsoft.com/en-us/dotnet/visual-basic/programming-guide/language-features/strings/using-regular-expressions-with-the-maskedtextbox-control

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Booney440