Ejabberd.Config.ValidatorUtility.put_error

You're seeing just the function put_error, go back to Ejabberd.Config.ValidatorUtility module for more information.
Link to this function

put_error(errors, key, val)

Specs

put_error(map(), atom(), any()) :: map()

Inserts an error inside the errors collection, for the given key. If the key doesn't exists then it creates an empty collection and inserts the value passed.