J.3.11 Preprocessing directives
The locations within #pragma directives where header name preprocessing tokens are recognized (6.4, 6.4.7).
How sequences in both forms of header names are mapped to headers or external source file names (6.4.7).
Whether the value of a character constant in a constant expression that controls conditional inclusion matches the value of the same character constant in the execution character set (6.10.1).
Whether the value of a single-character character constant in a constant expression that controls conditional inclusion may have a negative value (6.10.1).
The places that are searched for an included < > delimited header, and how the places are specified or the header is identified (6.10.2).
How the named source file is searched for in an included ” ” delimited header (6.10.2).
The method by which preprocessing tokens (possibly resulting from macro expansion) in a #include directive are combined into a header name (6.10.2).
The nesting limit for #include processing (6.10.2).
Whether the # operator inserts a \ character before the \ character that begins a universal character name in a character constant or string literal (6.10.3.2).
The behavior on each recognized non-STDC #pragma directive (6.10.6).
The definitions for __DATE__ and __TIME__ when respectively, the date and time of translation are not available (6.10.8).