Added clearer description of Optionals and Unwrapping. Minor typo changes as well.

swift.html.markdown

@@ -58,8 +58,9 @@ let piText = "Pi = \(π), Pi 2 = \(π * 2)" // String interpolation
 print("Build value: \(buildValue)") // Build value: 7
 
 /*
-    Optionals are a Swift language feature that allows you to store a `Some` or
-    `None` value.
+    Optionals are a Swift language feature that either contains a value, 
+    or contains nil (no value) to indicate that a value is missing. 
+    A question mark (?) after the type marks the value as optional.
 
     Because Swift requires every property to have a value, even nil must be
     explicitly stored as an Optional value.
@@ -75,11 +76,17 @@ if someOptionalString != nil {
     if someOptionalString!.hasPrefix("opt") {
         print("has the prefix")
     }
-    
+
     let empty = someOptionalString?.isEmpty
 }
 someOptionalString = nil
 
+/*
+    To get the underlying type from an optional, you unwrap it using the 
+    force unwrap operator (!). Only use the unwrap operator if you're sure 
+    the underlying value isn't nil.
+*/
+
 // implicitly unwrapped optional
 var unwrappedString: String! = "Value is expected."
 // same as above, but ! is a postfix operator (more syntax candy)
@@ -94,13 +101,13 @@ if let someOptionalStringConstant = someOptionalString {
 
 // Swift has support for storing a value of any type.
 // AnyObject == id
-// Unlike Objective-C `id`, AnyObject works with any value (Class, Int, struct, etc)
+// Unlike Objective-C `id`, AnyObject works with any value (Class, Int, struct, etc.)
 var anyObjectVar: AnyObject = 7
 anyObjectVar = "Changed value to a string, not good practice, but possible."
 
 /*
     Comment here
-    
+
     /*
         Nested comments are also supported
     */
@@ -296,10 +303,10 @@ print(numbers) // [3, 6, 18]
 // MARK: Structures
 //
 
-// Structures and classes have very similar capabilites
+// Structures and classes have very similar capabilities
 struct NamesTable {
     let names = [String]()
-    
+
     // Custom subscript
     subscript(index: Int) -> String {
         return names[index]
@@ -330,7 +337,7 @@ public class Shape {
 
 internal class Rect: Shape {
     var sideLength: Int = 1
-    
+
     // Custom getter and setter property
     private var perimeter: Int {
         get {
@@ -341,11 +348,11 @@ internal class Rect: Shape {
             sideLength = newValue / 4
         }
     }
-    
+
     // Lazily load a property
     // subShape remains nil (uninitialized) until getter called
     lazy var subShape = Rect(sideLength: 4)
-    
+
     // If you don't need a custom getter and setter,
     // but still want to run code before and after getting or setting
     // a property, you can use `willSet` and `didSet`
@@ -355,19 +362,19 @@ internal class Rect: Shape {
             print(someIdentifier)
         }
     }
-    
+
     init(sideLength: Int) {
         self.sideLength = sideLength
         // always super.init last when init custom properties
         super.init()
     }
-    
+
     func shrink() {
         if sideLength > 0 {
             --sideLength
         }
     }
-    
+
     override func getArea() -> Int {
         return sideLength * sideLength
     }
@@ -399,13 +406,13 @@ class Circle: Shape {
     override func getArea() -> Int {
         return 3 * radius * radius
     }
-    
+
     // Place a question mark postfix after `init` is an optional init
     // which can return nil
     init?(radius: Int) {
         self.radius = radius
         super.init()
-        
+
         if radius <= 0 {
             return nil
         }
@@ -459,7 +466,7 @@ enum Furniture {
     case Desk(height: Int)
     // Associate with String and Int
     case Chair(String, Int)
-    
+
     func description() -> String {
         switch self {
         case .Desk(let height):
@@ -498,7 +505,7 @@ protocol ShapeGenerator {
 
 class MyShape: Rect {
     var delegate: TransformShape?
-    
+
     func grow() {
         sideLength += 2
 
@@ -533,7 +540,7 @@ extension Int {
     var customProperty: String {
         return "This is \(self)"
     }
-    
+
     func multiplyBy(num: Int) -> Int {
         return num * self
     }