What does Dot "." operator use for in swift? is it to call a function? : <p>Just wanna know the usage of Dot operator in swift...</p>

<p>public func append(_ value: T) {</p>

<pre><code>     let newNode = Node(value: value)

      guard let tailNode = tail else {
        head = newNode
        tail = newNode
        return
    }

    newNode.previous = tailNode
    tailNode.next = newNode
    tail = newNode
}
</code></pre>
