syntax = "proto2";  // must be "proto2", proto3 requires enums starting with 0.

enum Enum
{
	enumerand = 1;  // must be non-zero
}

message Outer1
{
	message Inner
	{
		optional Enum enum1 = 1;  // can also be "required"
	}
}

message Outer2
{
	message Inner
	{
		// further trouble of this is also named "enum1"
		optional Enum enum2 = 1;  // can also be "required"

	}
}