// 1 .. all tags identical -> no need to merge, drop one
// 2 .. the unique tags match and there are some conflicting tags (same tag, different value) -> error, cannot be merged nor duplicated
// 3 .. there are some missing complementary tags and no unique conflict -> can be merged into a single line
// 1 .. all tags identical -> no need to merge, drop one
// 2 .. the unique tags match and there are some conflicting tags (same tag, different value) -> error, cannot be merged nor duplicated
// 3 .. there are some missing complementary tags and no unique conflict -> can be merged into a single line