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In the Pattern field in the Properties area, type your pattern using XML schema regular expressions. Check this site for more information. A simple example is a pattern that restricts a text control to only allow strings formatted as a US zip code: \d{5}|\d{5}-\d{4}. If you type this expression in the Patterns property, your form will permit values entered into this field only if they are five digits or five digits followed by the '-' character, followed by 4 digits.
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