As a user, I would not understand what this means. I had to read through the code to understand it.

Can we please reformulate as "Name of the INI-style section under which lines should be added (not including the [] brackets)"?

Also, since this technique is specific to INI-style sections, I think that it should be renamed to take this into account, so something like "file_ensure_lines_present_in_ini_section". Do you agree?