It seems that the use of macros/IFDEF (in any language, not just C) -- bifurcates into two distinct use-cases: 1) Platform/Processor/OS configuration/build use

It seems that the use of macros/IFDEF (in any language, not just C) -- bifurcates into two distinct use-cases: 1) Platform/Processor/OS configuration/build use-cases. (and) 2) All other use-cases that are not directly related to #1. In other words, if you're a future language designer and you design a macro system for your language, you might wish to distinguish between configuration/platform/build related macros -- and other macros not directly related to build and configuration... Doing that would allow one set and/or the other set to be selectively and easily evaluated back into the non-macro source of the base language -- depending on what is desired by the language user... Anyway, an excellent link!