Say you make a custom group called 'donator', and you have it inherit from 'user'. Then you make a group called 'vip' and make it inherit from 'donator'. In the inheritance tree, if you did "CheckGroup( "donator" )", 'donator' and 'vip' would be included. If you did "CheckGroup( "user" )" then 'user', 'donator', and 'vip' would be included, as well as every other group that, at one point, inherits from 'user'.