Some public forums exist to create a database of useful information. Stack Overflow is a good example of this type of forum. Since Stack Overflow is designed to be a repository of technical knowledge in Questions & Answer format, it’s important that conversations stay on-topic and are easy for users to find. In order to avoid topic drift, sites like this have very clear guidelines about avoiding topic drift that users must agree to before posting, and enable moderators to close a conversation to further replies once the key question has been answered.