Not only this, but the draft is contradicting in the use of Identifier.
Current definition goes:
An Identifier is either an http or https URI (commonly referred to as a URL within this document), or an account URI. This document defines various kinds of Identifiers, designed for use in different contexts.
String that uniquely characterize an entity in a specific environment with defined boundary conditions in which entities exist and interact
Note: this document defines various kinds of Identifiers, designed for use in different contexts. Examples includes https URLs and email addresses.
Above is the expansion of X.1254 | ISO 29115 (of identifier and context).