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# Customize regular expressions (Patterns) of a form's text box

###### If you want a text box in a form to accept only certain values or a certain number of characters, you need to set up a regular expression (Pattern) for each question. This is a very technical topic, so don't be afraid to reach out to our support team if you have any questions.

The programming language used for patterns is [Java](https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html).

In this example, we want the form to only accept letters (either uppercase or lowercase):

![](https://storage.crisp.chat/users/helpdesk/website/-/9/f/7/2/9f728b8c11d26000/c86ffaa5-b653-4be7-949d-600dd0_v6vnv.png =342xauto)

###### Simple examples:

![](https://storage.crisp.chat/users/helpdesk/website/-/7/6/8/f/768f2e7086e16800/e49b4337-73a9-41c4-83f6-789a19_12t0o3l.png =422xauto)

Now, you'll see a table with commonly used regular expressions (Patterns). You can find a more complete guide here: [Official regular-expression Java Patterns](https://www.w3schools.com/java/java_regex.asp)

![](https://storage.crisp.chat/users/helpdesk/website/-/3/6/e/4/36e45a2903994e00/1144de35-6b2f-4aa4-8328-ba41d5_11zd739.png =461xauto)

Don't hesitate to send us a message in the chat if you have any questions!