[dalke]

It appears to have a limited JS validator to prevent you from using anything other than the limited operators it allows.

[sp332]

It really doesn't like having anything after "return" except a single value or variable.

[dalke]

That's not it. For example, it accepts "return x|x&x;" . The restriction is that only a handful of Javascript operations are allowed. Anything else gives a hard-to-understand error message.