NOT11 — Syntactic category includes and \...Why?

Summary: Secondly, I"d like to have something clarified, if possible. The
syntactic category <Factor> includes <Ident> and \ <Ident>. What is the
reason for this? It seems to me that the only use for <Ident> in this
context is as a check for the existence of a runtime variable. $var is
used to denote the value of runtime variable var. However the "exist"
operator is used for this.

Would the semantics be any clearer if "$" was not used for runtime
variables at all? In this case a standalone <Ident> (not part of the
current event) would denote a variable.

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