How to make a binary XML file within android environment

I've been searching for a way to convert an ordinary XML into a binary one from within an Android app (into an AndroidManifest.xml file, to be more specific). I've found this which does the opposite of what I want, I've also found a way to do so but using APKTOOL on a PC.

There are some apps on the Play store such as this one that can create a binary AndroidManifest.xml, unfortunately they aren't open-source, so I thought I'd better ask someone about it.

Thanks