Conditional access was first introduced in Moodle 2.0 after being one of the most requested and voted for features in the Moodle 2.0 development list. At last, course developers have the power to ensure course participants meet criteria or set of criteria (by date, grade or activity completion - another great Moodle 2.0 addition) before they are able access a certain activity in their course.
Since conditional access was introduced, there has been gradual improvement in the functionality. First was to restrict access to sections and then that conditions could be based on data in participants’ profile fields thus allowing course developers to provide activities for specific students, e.g. from a particular department.
So, what are latest improvements? Until now you could only combine restrictions by adding them together - participants had to do one thing AND then another, e.g. viewing a Page resource AND adding a Forum post. In the latest version the OR operator can now be used and you can create more complex sets of conditions by nesting restrictions (having one condition within another)
Via Miloš Bajčetić