Annex G (informative) Ill-formed, no diagnostic required [ifndr]

G.11 [cpp]: Preprocessing directives [ifndr.cpp]

G.11.3[ifndr:cpp.include.malformed.headername]
Specified in: [cpp.include]

If the header-name-tokens after an include directive cannot be formed into a header-name (with implementation-defined treatment of whitespace), the program is ill-formed, no diagnostic required.
[Example 1: #include// IFNDR, does not match one of the two allowable forms — end example]