is usually
     ‘binary’ or non-printable).  Exceptions are well-known file formats (core
     files, tar archives) that are known to contain binary data.  When adding
     local definitions to /etc/magic, make sure to preserve these keywords.
     Users depend on knowing that all the readable files in a directory have
     the word ‘text’ printed.  Don't do as Berkeley did and change ‘shell
     commands text’ to ‘shell script’.

     The filesystem tests are based on examining the return f