"But I don't follow the 'affects semantics?' column."
I think it means whether the parsing happens before macros are run or not. In Arc, ssyntax happens after macros, so macros can affect the meaning/behavior of ssyntax. In most Lisps, syntax is read before macros, so macros can't change the meaning.
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Ah yes, Nulan has changed since that page was added, I'll go in and update it...
