JSqueeze claims to be PSR-0 (in its composer.json), but it really isn't:

https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-0.md

"A fully-qualified namespace and class must have the following structure \<Vendor Name>\(<Namespace>\)*<Class Name>"

that is, at least one level of namespacing is required, a top-level 'Vendor Name'. JSqueeze is a bare class. I'm now in an argument with my downstream package reviewer because our distribution guidelines don't allow us to put libraries directly in /usr/share/php (to avoid mess and conflicts - nothing else is called JSqueeze yet, but just today I found two things called cssmin, for instance...), but if I put it in a subdirectory, nothing will be able to autoload it without patching.