The FileMaker Data Migration Tool Guide lists one of the command line options as
The description for this option is
Doesn't check the font mapping for field contents
Does anyone know what this means?
IDK the answer, but remember that the field (or text) on the layout can have formatting (styles, including font) applied in Layout Mode. In addition the values in the field (or merge field), may have styles applied (and stored) by user entry and/or calculation (see the text formatting functions).
I wonder if the "themes" styling (font) is honored by this but the user/calculated style is ignored?
The short / simplified answer is...
Checking to see if the font style in "FieldA" in the original file is the same as the font style in "FieldA" in the clone that is being used to migrate and create a new file.
The slightly more involved answer is...
For solutions with a "few" fields / records, this is probably not that big a deal. But if you have a lot of tables and a lot of fields and records and have made font changes in many of them, it would take time for FileMaker to check every field and every record to see if the "style" of said field has changed from record to record and therefore it would slow down the migration process to do all those checks.
The "-ignore fonts" option bypasses this style check. So, if you have not done any font style changes OR you do not care if any font style changes are brought over to your new file than you can disable the check with the "-ignore_fonts" option.
Retrieving data ...