I have seen both present and perfect forms of the conjunctive for negative orders or requests, for example ne canas and ne cecineris. What is the difference? Is one more an order and the other more a request? Are they interchangeable?
I am interested in these as orders, either as separate exclamations or as part of a governing clause, not subordinate to anything else. The standard I have learned for negative imperative is either noli(te) with infinitive or ne with perfect conjunctive. I have the impression that ne with present conjunctive is more of a request, but I am unsure.
There is a similar earlier comparison for hesitation, but it does not cover orders or requests.