removing comments and white-spaces, obfuscates local variables using
the smallest possible variable name. This obfuscation is safe, even
when using constructs such as 'eval' or 'with' (although the
compression is not optimal in those cases) Compared to jsmin, the
average savings is around 20%.
The YUI Compressor is also able to safely compress CSS files. The
decision on which compressor is being used is made on the file
extension (js or css).