What is the difference between Expression.Variable() and Expression.Parameter()?

Expression.Variable is used to declare a local variable within a block. Expression.Parameter is used to declare a parameter for an incoming value.

Now currently C# doesn't allow statement-bodied lambda expressions, but if it did, imagine:

// Not currently valid, admittedly...
Expression<Func<int, int>> foo = x =>
{
    int y = DateTime.Now.Hour;
    return x + y;
};

If this were valid, the C# compiler would generate code using Expression.Parameter for x, and Expression.Variable for y.

At least, that's my understanding. It's a real shame that the documentation for the two methods is basically the same :(