When I look at the theme options of Vanilla, in unchanged condition, I see three tabs under which several options can be set.
When I look at the file options.twig in the options directory of the theme (after copying theme from the original to the extented theme), I see that these files to not correspond to what is shown in the theme settings page.

Where do the theme options of Vanilla and of extensions of come from? I know I can define several options in de config.xml file, but how does the settings page get build up?