> ## Knowledge Base Index
> Fetch the complete knowledge base index at: https://staging.chrisp.chat/sitemap.xml
> Use this file to discover available pages before exploring further.
> Pure-Markdown content can be obtained by appending a '.md' suffix to the content URLs listed in the sitemap (without the trailing slash).

# 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/-/3/e/4/4/3e4414829eb8c000/b4a6b256-ddff-48b5-b6a1-31578b_1c27a9y.png)

****Simple examples:****

![](https://storage.crisp.chat/users/helpdesk/website/-/1/3/8/1/13815c5e7de8d100/10486ed4-febf-4b28-96a5-318e59_8mh8th.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/-/3/9/4/a/394a77045d61580/78871993-44db-4784-9992-da78a0_1drjpyx.png)

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