///testrest("arg1");
arg1
undefined
///(contents of rest...)
0
///testrest("arg1", "arg2", "arg3");
arg1
arg2
///(contents of rest...)
1
arg3
///testrest("arg1", "arg2", "arg3", "arg4", "arg5");
arg1
arg2
///(contents of rest...)
3
arg3
arg4
arg5
///Array.prototype.test = "test";
///rest.test
test
