Android reengineering : extract and protect APK's resources (technical questions)

I'm interested in the technical details of APK files. I know already that the APKTOOL is a开发者_运维百科ble to extract all those layout files and so on of an APK file (including the smali sources), but I would like to khow, how the APKTOOL does the extraction of layouts, since they are crypted somehow (in case that you open it with unzip).

Does anybody know something about how Android compresses/encrypts(?) those layout files in the APK files? Is there any description out there?

Does anybody know a way to protect layouts against reengineering? (similar to ProGuard used for the source code)?

As far as I know, all xml files in APKs are stored in Binary XML format. So they aren't encrypted and that's not a big deal to read them.

What about protection, I don't think there's a way to obfuscate them somehow. The only way to make layouts difficult for reading is to create view directly from code, but I don't think you should do it.