ShowUserGroups displays a list of all groups a user is in on their user page, below the page heading.
Note that the '*' and 'user' groups are not displayed as they are redundant (all users are a member of these groups).
Sorting the groups
An optional function can be defined in a user/site JS page to sort the user groups as you wish. The compare function will be supplied to Array.prototype.sort to be used on the array containing the user groups. It should be defined in the global scope, and be named ShowUserGroups_sorter. For detailed info on how this compare function should work, see the MDN page for Array.prototype.sort().