Don’t worry about the ‘INI’ file.
The wording in that section is somewhat out of date.
It is also plain wrong in some places !
Sketchup.read_default and Sketchup.write_default methods are ways of writing and reading your own values globally, stored with SketchUp itself rather than your model or session.
They are saved in various ways depending on your OS and SketchUp version - registry/plist and more recently json files in the user’s tree…
The ‘writing’ simply has three arguments [similar to attribute dictionaries]
Sketchup.write_default(section, key, value)
The ‘reading’ has three*** [again similar to attribute dictionaries]
value = Sketchup.read_default(section, key, default_value)
***If ‘default_value’ is omitted and the key is not defined it will then return nil
The ‘section’ is your own tool’s ‘name’ string.
The ‘key’ is your own named-key string.
The ‘value’ can be most of the usual formats available to attribute dictionaries.
Although the values are always stored as ‘text’ strings, the reading process should convert them back to their original format - so 1.234 writes >>> “1.234” then it reads >>> 1.234