Node.set_cookie

You're seeing just the function set_cookie, go back to Node module for more information.
Link to this function

set_cookie(node \\ Node.self(), cookie)

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Specs

set_cookie(t(), atom()) :: true

Sets the magic cookie of node to the atom cookie.

The default node is Node.self/0, the local node. If node is the local node, the function also sets the cookie of all other unknown nodes to cookie.

This function will raise FunctionClauseError if the given node is not alive.