To inject some data into the .fio header, the FioAdditions environment variable has to point to a Python file generating output.

p09/door/haso107d1.01 [4]: lsenv
                         Name                                                         Value   Type
 ---------------------------- -------------------------------------------------------------- ------
                 FioAdditions                                         /online_dir/    str

The output of FioAdditions can be: list, dict, [list], [dict], [list, dict], [dict, list]. 'list' is always understood as list of strings.

Lists of strings are stored in the comment section of the header, dictionaries in the parameter section.