Kernel.SpecialForms.__block__

You're seeing just the macro __block__, go back to Kernel.SpecialForms module for more information.
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__block__(args)

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Internal special form for block expressions.

This is the special form used whenever we have a block of expressions in Elixir. This special form is private and should not be invoked directly:

iex> quote do
...>   1
...>   2
...>   3
...> end
{:__block__, [], [1, 2, 3]}