I already feared the term “blob” could lead to confusion. The blob type you refer to is the super type of atoms that is used to encapsulate arbitrary binary data (often handles to streams, threads, clauses, etc). Strings, floats, big integers and rational numbers live on the (global) stack and are internally called indirect types and are also blobs in the sense that the content of these types is simply an array of binary data. As yet, it is not possible for the user to add new types to this mechanism as it is for blobs (and there are no plans to change that either).