...Sometimes, receiving input in a HTTP request isn't only about making sure that the data is in the right format, but also that it is free of noise. validator.js provides a handful of sanitizers that can be used to take care of the data that comes in. Although express-validator offers plenty of handy validators and sanitizers through its underlying dependency validator.js, it doesn't always suffice when building your application. For these cases, you may consider writing a custom validator or a custom sanitizer. A custom validator may be implemented by using the chain method .custom(). It takes a validator function.