Сейчас зелез в С99
6.4 Lexical elements
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4 If the input stream has been parsed into preprocessing tokens up to a given character, the
next preprocessing token is the longest sequence of characters that could constitute a
preprocessing token. There is one exception to this rule: a header name preprocessing
token is only recognized within a #include preprocessing directive, and within such a
directive, a sequence of characters that could be either a header name or a string literal is
recognized as the former.5 EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not a
valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex
might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the program
fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or
not E is a macro name.
6 EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on
increment operators, even though the parse x ++ + ++ y might yield a correct expression.
