GitLab currently uses a regex to validate group names.
It has proved difficult to prevent XSS problems. In trying to
chase XSS issues we've tightened the regex and don't allow
some completely benign characters on their own, such as
parentheses. This results in a worse user experience and may not
really protect from XSS. Instead, this now uses the
Rails::Html::FullSanitizer to validate group names.