1
As I learned, xoops_isadmin is true only for users, which have any rights in administration of XOOPS system.
And it give me two problems
1. Pure module's admins haven't "Administration" link in User menu
2. If I want enable to module's admin some additional right on site, I have to do it with each admin's group (my config isn't "standard" - each module have separate group in members groups, in which I add modules's admins and I have ~30-40 modules om my test site), and it's long-time and not bullet-proof solution.
$xoops_ismoduleadmin = 1 for any user, added to any group with administration access to some module can solve my problem (and I think, can be usable in common for all)