insert script vs start using stack questions

[Doug Lerner]

(1) What is the difference between
    insert script of stack "mainstack"
and
    start using stack "mainstack"
?

(2) I added 

    insert script of stack "mainstack"

to the preOpenStack handler for a stack. But a handler call in the stack
caused an error saying it couldn't find the handler. Shouldn't it though?

(3) Do repeated "start using" or "insert script" calls mean anything, or are
they like "global" calls that affect all stacks after the call?

doug