Distinction between ' and " usage in Elixir?

apostrophe-diff-than-quot

What are the "rules" or guidelines for using ' vs " in Elixir?

iex> l1 =['test']
['test']
iex> l2 = ['test']
['test']
iex> l1 == l2
true
iex> l3 = ["test"]
["test"]
iex> l1 == l3
false
iex> s1 = 'test'
'test'
iex> s2 = 'test'
'test'
iex> s3 = "test"
"test"
iex> s1 == s2
true
iex> s1 == s3
false