Labels are created with a parent context, which is either a code attribute or a code builder. A label originating in a code attribute context may be reused in a code builder context, but only labels from a single code attribute may be reused by a single code builder. Mappings to and from BCI are the responsibility of the context in which it is used; a single word of mutable state is provided, for the exclusive use of the owning context. In practice, this means that labels created in a code attribute can simply store the BCI in the state on creation, and labels created in in a code builder can store the BCI in the state when the label is eventually set; if a code attribute label is reused in a builder, the original BCI can be used as an index into an array.