What's the connection between 'user groups' and 'user ranks'?

Ranks are a label and not in any way connected to user group permissions. You can, however, make a user group called, for example "Moderators" and place the moderators in that group - and set each user's rank to "Moderator"

User groups control permissions for access within the website, ranks are simply a label that can be assigned to any user. When users are put in certain groups, it maybe useful to give them a rank or identifier if they have a certain role in the management of the website.

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