[lispm]

> textual representation is irrelevant to the semantics of the program

It's not completely irrelevant, since Common Lisp has the idea of a text-based file with source code and a compilation mode for it (-> COMPILE-FILE).

But generally what you say is true. We see that especially in two places: 1) the Lisp interpreter, which runs non-text s-expressions and 2) special development environments, like Interlisp-D/Medley where a prominent way to edit Lisp code is a structure editor, which manipulates s-expressions in memory.