Where is the documentation for the processing of ordinary character encoding by GCC or Clang available?

edit

The documentation for the processing of ordinary character encoding by GCC or Clang would be available in their respective user manuals or documentation.

For GCC, this information can be found in the GCC Manual, specifically in the sections on Character Sets and Character Escapes.

For Clang, this information can be found in the clang User Manual, specifically in the sections on Source Code Representation and Character Literals.