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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/-/a/6/2/2/a622c5970bc94800/9e6f1f86-e73d-44e2-8276-db5a19_1mei7s6.png)

****Simple examples:****

![](https://storage.crisp.chat/users/helpdesk/website/-/6/e/1/5/6e158c40308d5800/f0cc38b9-efee-43bf-9ca4-b77022_goxdi8.png)

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://storage.crisp.chat/users/helpdesk/website/-/c/e/2/c/ce2c09cd8d7ca800/5d2f827d-4295-454c-b541-30853c_5x8mx.png)

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