I need clarification on this loop. I don't quite understand how the for loop iterates over 3 x and y values.

init(x: Int, y: Int) {
    self.x = x
    self.y = y

}


let x: Int // these *stored properties* have no value assigned to them - that comes later
let y: Int // their job is to name the constant, and define its type.

/// Returns the surrounding points in range of
/// the current one
func points(inRange range: Int = 1) -> [Point] {    // Here we are creating a new function within the struct, with a default value of 1
    // We have then specified the return type as being an array of Point instances

    var results = [Point]() // Here we declare a new variable of type Point, and assign an empty array. We'll eventually assign
    // coordinates to this array. It's a variable because we need to mutate it throughout this process.

    let lowerBoundOfXRange = x - range // get the lower bound numbers of the origin x point and assign them to a constant
    let upperBoundOfXRange = x + range // get the upper bound numbers of the origin x point and assign them to a constant

    let lowerBoundOfYRange = y - range // get the lower bound numbers of the origin y point and assign them to a constant
    let upperBoundOfYRange = y + range // get the upper bound numbers of the origin y point and assign them to a constant

    /*
     now we start a loop which will go through all of the x values and y values and create a new constant containing the values based on the custom type Point. this constant is then added (appended) to the above "results" variable, and the loop continues until all points have been collected and added to the results array.
     */
    for xCoordinate in lowerBoundOfXRange...upperBoundOfXRange {
        for yCoordinate in lowerBoundOfYRange...upperBoundOfYRange {
            let coordinatePoint = Point(x: xCoordinate, y: yCoordinate)
            results.append(coordinatePoint)
        }
    }

    return results // finally, the function returns the results array ready for calling back later
}