Quercus is an implementation of PHP written in Java, and released under the GPL.
If I use it, does my PHP code fall under the GPL?
What about my Java code?
Assuming I write new Java code, and new PHP code, and use Quercus to run my PHP code on the JVM and call into my Java code, which pieces fall under the GPL?
Also, assume that the result is commercial software that I want to distribute.