would parse each line in myfile.txt, ignoring lines that begin with a semicolon, passing the 2nd and 3rd token from each ...

    would parse each line in myfile.txt, ignoring lines that begin with
    a semicolon, passing the 2nd and 3rd token from each line to the for
    body, with tokens delimited by commas and/or spaces.  Notice the for
    body statements reference %%i to get the 2nd token, %%j to get the
    3rd token, and %%k to get all remaining tokens after the 3rd.  For
    file names that contain spaces, you need to quote the filenames with
    double quotes.  In order to use double quotes in this manner, you also
    need to use the usebackq option, otherwise the double quotes will be
    interpreted as defining a literal string to parse.

    %%i is explicitly declared in the for statement and the %%j and %%k
    are implicitly declared via the tokens= option.  You can specify up
    to 26 tokens via the tokens= line, provided it does not cause an
    attempt to declare a variable higher than the letter 'z' or 'Z'.
    Remember, FOR variables are single-letter, case sensitive, global,
    and you can't have more than 52 total active at any one time.

    You can also use the FOR /F parsing logic on an immediate string, by
    making the file-set between the parenthesis a quoted string,
    using single quote characters.  It will be treated as a single line
    of input from a file and parsed.

    Finally, you can use the FOR /F command to parse the output of a
    command.  You do this by making the file-set between the
    parenthesis a back quoted string.  It will be treated as a command
    line, which is passed to a child CMD.EXE and the output is captured
    into memory and parsed as if it was a file.  So the following
    example:

      FOR /F "usebackq delims==" %%i IN (`set`) DO @echo %%i

    would enumerate the environment variable names in the current
    environment.