I just modifying / simplifying one quite complex points file. There are few lines which I don’t understand, I would like to keep things simple , but I wouldn’t like to broke some useful functionality.
The cityxx thing is an internal flag that whoever wrote this file is using to avoid applying the same rule twice. Basically it applies the rule, then sets cityxx to yes, which stops the rule then being applied again to the same object.
The other things you pick out are doing the same thing. They are internal flags being used by the style-writer to control how rules are applied to objects.
Well that code is literally just setting a flag called 20resolution to yes. Somewhere else, there’ll be some code that actually does something interesting when the 20resolution flag is set to yes.