[Rd] Making parent.env<- an error for package namespaces and package imports

I'd like to propose a change to the R language so that calling 'parent.env<-' on a package namespace or package imports is a runtime error. Currently the documentation warns that it's dangerous behaviour and might go away: The replacement function ‘parent.env<-’ is extremely dangerous as

Re: [Rd] Advice on package design for handling of dots in a formula

There is the issue of best design and the issue of dots, which I think are separate. As to the dots, I don't think there is any way out but to handle it yourself. The formula parser has defined "." to mean everything in the frame that is not listed in the response. For good or ill it allows