Is "a+++i" equal to "(a++)+i"

C11 standard, part 6.4 (Lexical elements)/4 says (and in C99 it's the same):

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 also an example there:

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.