You shoul set Format property to 'R' and remove '-' from the textbox value.

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>I have a textbox that has a value of 9999-8000
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>I would like to apply the following input mask dynamically '99999-999'
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>I am expecting the output to be '99998-000' but it gives an output of '9999--000'
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>how can I format the output to get '99998-000'
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