By default, the compiler accepts the language as specified in [PIM3]. For compatibility with older sources, m2c supports also the options -r0 and -r1 which switch to [PIM1] and [Wirth94], respectively. [PIM4] and the upcoming ISO-standard for Modula-2 are not supported and probably will never be.
The following paragraphs follow roughly the Modula-2 report in [PIM3] - the number in the header specifies the corresponding section.