Translations:Participant settings/13/en
From LimeSurvey Manual
Allow public registration
If you use tokens to control access to your survey, the only people who can use the survey are those who have an entry and a unique token allocated in the survey participants table. If you would like to use tokens, but also allow public registration, set this to "Yes". The "Yes" setting will allow a visitor to register his name and email address. This will create a new entry in your survey participants table for this person, then send them an invitation email. The application's backend ensures that only one person per email address can complete your survey. If a visitor tries to register for the second time with the same email address, they will not receive another email.