Actually the problem here has to do with the scope where the declaration happens. If redeclaration happened as mentioned in your quoted text ie. assignment of a

Actually the problem here has to do with the scope where the declaration happens. If redeclaration happened as mentioned in your quoted text ie. assignment of a new value, there would be no problem. As is [in a different scope], a redeclaration of err is actually a declaration of a shadowed err variable.