Understanding List Appending in Elixir

The content revolves around a query by retake_chancy about why the expression `[a | 4]` does not produce the list `[1, 2, 3, 4]` and the need to use the concatenation operator `++` instead in Elixir. The explanation provided delves into the nature of 'proper lists' in Erlang and Elixir, detailing that lists are essentially constructed with an element followed by another list, thus `[0 | [1, 2, 3]]` works while `[[1, 2, 3] | 4]` does not. Further elaboration is provided in the comments, referencing Erlang and Elixir documentation and additional resources for understanding list mechanics.