Here I'm talking about the value of one particular claim: `scope`. If you identify each scope by only one character it would be limited to the size of your alphabet.

If you talk about claim names, they basically aim to be short. For instance, claims defined in RFC7519 Section 4.1 (https://tools.ietf.org/html/rfc7519#section-4.1) are only 3 characters long. As explained in the same section:

  "All the names are short because a core goal of JWTs is for the representation to be compact."