Both points are related and matter.

For most purposes, not being able to access something, and being able to access something not officially in an interface, where doing so introduces an unpredictable breaking dependency, the practical result is the same: You can't (actually/sensibly) do it.

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zabzonk an hour ago | parent [-]

Then why not define "something" as static, which makes the compiler and linker guarantee that you can't do it?

	▲	bigfishrunning an hour ago \| parent [-]
		What if I want to internally access it from multiple compilation units, but not necessarily encourage downstream users from using it? This is really common.