In /proc/$PID/smaps in the VmFlags what is the difference between "readable" and "may read"?

The man page describes the meaning of the VmFlags:

The "VmFlags" line (available since Linux 3.8) represents
              the kernel flags associated with the virtual memory area,
              encoded using the following two-letter codes:

                     rd   -   readable
                     wr   -   writable
                     ex   -   executable
                     sh   -   shared
                     mr   -   may read
                     mw   -   may write
                     me   -   may execute
                     ms   -   may share

What is the difference between "readable" and "may read"? Those seem equivalent. Same for the write/executable/share versions.