Well, "available" is a bit debatable, as the code determines some of the logic around permissions. And what you can and/or should do with permissions is quite a long discussion too.
But the coder's technical answer is: https://docs.atlassian.com/jira/latest/com/atlassian/jira/webtests/Permissions.html - that's the list for 6.4, it should be updated for 7 soon.
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