That's a prefix code, they're defined by no code word being a prefix of another (so if you put them in a trie the code words only appear on leaves). A trivial

That's a prefix code, they're defined by no code word being a prefix of another (so if you put them in a trie the code words only appear on leaves). A trivial example is the reverse: _. _.. _... Which can be decoded by, at worst, reversing the string first. (Sorry if I've misunderstood your example)