Difference between scope of block yield variable between for-in and Enumerable#each

gistfile1.txt

array = [1,2,3,4]

array.each do |array_iter|
  # do something with array_iter
end

# Hmm, array_iter isn't defined
puts defined?(array_iter)

for for_iter in array do
  # do something with for_iter
end

# Hmm, for_iter *IS* defined
puts defined?(for_iter)

I found this out by looking at some commits where the author was changing for loops to Array#each, and I wondered what the distinction was; "The moar u know!".