# Regular expressions

Some fields on the Trustelem administration pages allow the usage of regular expressions.

* In **redirect_uri**, for indicating multiple possible values

    For example, the following code allows a URL with an optional port number and trailing:

    ```regexp
    regexp+http://localhost(:(\d)+)?/
    ```

* In the applications **scripts**, for modifying the returned attributes

    For example, the following code changes the domain name in email addresses:

    ```regexp
    return user.email.replace(/([^@])@./, '$1@mondomaine.io');
    ```