HOWTO: Port a C/C++ Library to JavaScript (xml.js)

I've been porting various libraries to JavaScript recently (lzma.js, sql.js) and I thought it might be useful to write up details about how this kind of thing is done. So here is how I ported libxml - an open source library that can validate XML schemas - in response to a request. Note that this isn't a general HOWTO, it's more a detailed writeup of what I did to port libxml in particular, but I