7
the -1 = disabled is - so far - a XOOPS 2.2-only level.
Apart from that, you should only worry about 0 (not activated) and >0 (activated). Level 5 is given to the user created through the setup process, but is effectively the same as level 1.
My guess is that it is a leftover from earlier days, when the group permissions were not as good as they are today and we needed a way to specify an administrator specifically on the user profile.
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Cusix Software