This same blog has a post on the idiosyncrasies of the C preprocessor. Reminds me of several convoluted macros I assembled to stress test a C/C++ static analyzer at my last job. My favorite that I wrote was the following, combining line continuations, trigraphs, digraphs, universal character names, and block comments. Particularly insidious is the line continuation between / and * in the block comment. It is equivalent to: #define 🇩🇪() "de"

   ??/
  %: \
  /??/
  */*\
  **/\
  def\
  ine\
   \U\
  0??/
  001\
  F??/
  1E9\
  ??/\
  U00\
  01F\
  1EA\
  (??/
  ) "\
  de"\

This example also exposes undefined behavior from the C++ standard: "if a splice results in a character sequence that matches the syntax of a universal-character-name, the behavior is undefined" [0].

[0]: https://eel.is/c++draft/lex.phases#1.2