A programmer may want to place two question marks together yet not have the compiler treat them as introducing a trigraph. The C grammar does not permit two consecutive codice_22 tokens, so the only places in a C file where two question marks in a row may be used are in multi-character constants, string literals, and comments. This is particularly a problem for the classic Mac OS, where the constant codice_23 may be used as a file type or creator. To safely place two consecutive question marks within a string literal, the programmer can use string concatenation codice_24 or an escape sequence codice_25.