Regarding the "preferred hostnames" section here:
https://docs.cloud.mongodb.com/tutorial/manage-group-settings/#group-settings

After the last line, "To specify a pattern for the hostname, use the Ends With or Regex buttons.", it would be excellent to add a clarifying statement that regex usage desiring a "starts with" behavior must be sure to add a .* at the end in order to correctly match. For example, if you wanted preferred hostnames that started with "acme-", the regex would be

^acme-.*