To help with the 'as is' part, I've provided some similar sentences, maybe if you understand those, you can start to understand the way it is written in the book. Due to the custom of the East being a certain way, his feet were bound... It is the custom of the East to do this, so his feet were bound... As the custom of the East is to bind his feet, they did so... Just like the custom of the East, his feet were bound... Or maybe these help: As X is Y = because X and Y are the same As is X, so is Y = Just like X, Y is a certain way The use of 'as is' in this context is quite hard to explain. Hope I helped you a little bit :)

Custome here means the way the culture of the area, or group of people does a certain thing. Where I live when people drive past me when I'm outside in my yard they often wave. It is a custom in small towns, or rural areas in my state to do this.