In Koha 3.0, “events” that cause a problem in circulation results in, either “issue forbidden” or “issue needs confirmation”. However, the result is hardcoded : for example book being reserved results in “needs confirmation”, and item notforloan results in “issue impossible”. Some libraries want a fine tuning possibilities for all rule.
So, BibLibre plans to add the feature through systempreferences. For each issuing constraint, a system preference will let the library decide wether a confirmation is asked or the issue is forbidden.
Note that some contraint already have such a syspref, like the maxoutstanding.