There are several ways how plugins may generate or interact with content
 Such slots can be defined in template.php using gpOutput::Get('Extra', 'Area-Name') for 'Extra Content', predefined settings.php-based Areas gpOutput::GetArea('Area-Id', 'Content'), or menus via gpOutput::Get('Menu');
 Plugins may also add content directly to this area via the GetContent_After hook.
Has it been thought about creating a more detailed documentation for Typesetter
Oh yes, it has been thought a thousand times.
Ok, seriosly. I have started such thing about 1 year ago but it's still only a fraction of what it should be. Still needs some 100 hours at minimum before I can make it public.