A permission is a part of a role which allows or denies a someone to use a feature or function of Moodle.  There are over 450 different permissions settings in any Moodle role.   Each permission has 1 of 4 states that can be assigned to it: "not set", "allow", "prevent", and "prohibit.  Editing or creating new roles on the site level can be complicated. In part because of the hierarchical nature of contexts.  In many contexts, roles or permissions can be overridden, and the permitted user will see a shortened list of permissions appropriate to the context.

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