# 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'); ```