Silly shell question

[Swift Griggs <swiftgriggs%gmail.com@localhost>]

In ksh, when you use the 'export' keyword, what is actually going on? Does 
it create a copy of the variable in memory? I doubt it since I tried a 
test and I could see the exported version changing even if I just change 
the original variable:

# FOO=abc
# export FOO
# ksh
# echo $FOO
abc
# exit
# FOO=123
# ksh
# echo $FOO
123
# exit

So, what is that really happens with exported variables? Does the 
shell/app that's starting up check for exported variables and somehow 
import them? How can it tell? I noticed there are a LOT of checks around 
exported variables in ast-ksh. It appears to be a dangerous proposition in 
some cases.

Sorry if this seems like a dumb question. I'm just curious about the 
intrinsics of how it works. I looked at the source code for ast-ksh, but 
it's pretty huge and hard to follow to answer this question. I'm just 
wondering what the key mechanism is. Curiosity only.

-Swift