When creating an executable jar (one that can be kicked off with -jar), make sure that the Main-Class entry ends with a line separator. If you accidentally type a space after the class name, it won’t work; you’ll get a NoClassDefFoundError when trying to execute against the jar.
Shades of makefile spaces instead of tabs problems. Developers that build space-specific code should be shot. If you want to make your code whitespace-specific, you should have to write it in the Whitespace language.