diff --git a/Sources/HummingbirdMustache/Lambda.swift b/Sources/HummingbirdMustache/Lambda.swift
index 5bb3e3f..58b32ae 100644
--- a/Sources/HummingbirdMustache/Lambda.swift
+++ b/Sources/HummingbirdMustache/Lambda.swift
@@ -1,2 +1,36 @@
 
-public typealias HBMustacheLambda = (Any, HBMustacheTemplate) -> String
+/// Lambda function. Can add this to object being rendered to filter contents of objects.
+///
+/// See http://mustache.github.io/mustache.5.html for more details on
+/// mustache lambdas
+/// e.g
+/// ```
+/// struct Object {
+///     let name: String
+///     let wrapped: HBMustacheLambda
+/// }
+/// let willy = Object(name: "Willy", wrapped: .init({ object, template in
+///     return "<b>\(template.render(object))</b>"
+/// }))
+/// let mustache = "{{#wrapped}}{{name}} is awesome.{{/wrapped}}"
+/// let template = try HBMustacheTemplate(string: mustache)
+/// let output = template.render(willy)
+/// print(output) // <b>Willy is awesome</b>
+/// ```
+///
+public struct HBMustacheLambda {
+    /// lambda callback
+    public typealias Callback = (Any, HBMustacheTemplate) -> String
+
+    let callback: Callback
+
+    /// Initialize `HBMustacheLambda`
+    /// - Parameter cb: function to be called by lambda
+    public init(_ cb: @escaping Callback) {
+        self.callback = cb
+    }
+
+    internal func run(_ object: Any, _ template: HBMustacheTemplate) -> String {
+        return callback(object, template)
+    }
+}
diff --git a/Sources/HummingbirdMustache/String.swift b/Sources/HummingbirdMustache/String.swift
new file mode 100644
index 0000000..eba3037
--- /dev/null
+++ b/Sources/HummingbirdMustache/String.swift
@@ -0,0 +1,23 @@
+
+extension String {
+    private static let htmlEscapedCharacters: [Character: String] = [
+        "<": "&lt;",
+        ">": "&gt;",
+        "&": "&amp;",
+    ]
+    /// HTML escape string. Replace '<', '>' and '&' with HTML escaped versions
+    func htmlEscape() -> String {
+        var newString = ""
+        newString.reserveCapacity(self.count)
+        // currently doing this by going through each character could speed
+        // this us by treating as an array of UInt8's
+        for c in self {
+            if let replacement = Self.htmlEscapedCharacters[c] {
+                newString += replacement
+            } else {
+                newString.append(c)
+            }
+        }
+        return newString
+    }
+}
diff --git a/Sources/HummingbirdMustache/Template+Render.swift b/Sources/HummingbirdMustache/Template+Render.swift
index 5499e1f..0d72411 100644
--- a/Sources/HummingbirdMustache/Template+Render.swift
+++ b/Sources/HummingbirdMustache/Template+Render.swift
@@ -1,5 +1,10 @@
 
 extension HBMustacheTemplate {
+    /// Render template using object
+    /// - Parameters:
+    ///   - object: Object
+    ///   - context: Context that render is occurring in. Contains information about position in sequence
+    /// - Returns: Rendered text
     func render(_ object: Any, context: HBMustacheContext? = nil) -> String {
         var string = ""
         for token in tokens {
@@ -11,7 +16,7 @@ extension HBMustacheTemplate {
                     if let template = child as? HBMustacheTemplate {
                         string += template.render(object)
                     } else {
-                        string += htmlEscape(String(describing: child))
+                        string += String(describing: child).htmlEscape()
                     }
                 }
             case .unescapedVariable(let variable, let method):
@@ -34,7 +39,13 @@ extension HBMustacheTemplate {
         }
         return string
     }
-    
+
+    /// Render a section
+    /// - Parameters:
+    ///   - child: Object to render section for
+    ///   - parent: Current object being rendered
+    ///   - template: Template to render with
+    /// - Returns: Rendered text
     func renderSection(_ child: Any?, parent: Any, with template: HBMustacheTemplate) -> String {
         switch child {
         case let array as HBMustacheSequence:
@@ -42,7 +53,7 @@ extension HBMustacheTemplate {
         case let bool as Bool:
             return bool ? template.render(parent) : ""
         case let lambda as HBMustacheLambda:
-            return lambda(parent, template)
+            return lambda.run(parent, template)
         case .some(let value):
             return template.render(value)
         case .none:
@@ -50,6 +61,12 @@ extension HBMustacheTemplate {
         }
     }
     
+    /// Render an inverted section
+    /// - Parameters:
+    ///   - child: Object to render section for
+    ///   - parent: Current object being rendered
+    ///   - template: Template to render with
+    /// - Returns: Rendered text
     func renderInvertedSection(_ child: Any?, parent: Any, with template: HBMustacheTemplate) -> String {
         switch child {
         case let array as HBMustacheSequence:
@@ -62,7 +79,8 @@ extension HBMustacheTemplate {
             return template.render(parent)
         }
     }
-    
+
+    /// Get child object from variable name
     func getChild(named name: String, from object: Any, method: String?, context: HBMustacheContext?) -> Any? {
         func _getChild(named names: ArraySlice<String>, from object: Any) -> Any? {
             guard let name = names.first else { return object }
@@ -78,6 +96,9 @@ extension HBMustacheTemplate {
             return _getChild(named: names2, from: childObject!)
         }
 
+        // work out which object to access. "." means the current object, if the variable name is ""
+        // and we have a method to run on the variable then we need the context object, otherwise
+        // the name is split by "." and we use mirror to get the correct child object
         let child: Any?
         if name == "." {
             child = object
@@ -87,6 +108,8 @@ extension HBMustacheTemplate {
             let nameSplit = name.split(separator: ".").map { String($0) }
             child = _getChild(named: nameSplit[...], from: object)
         }
+        // if we want to run a method and the current child can have methods applied to it then
+        // run method on the current child
         if let method = method,
            let runnable = child as? HBMustacheMethods {
             if let result = runnable.runMethod(method) {
@@ -95,23 +118,5 @@ extension HBMustacheTemplate {
         }
         return child
     }
-
-    private static let htmlEscapedCharacters: [Character: String] = [
-        "<": "&lt;",
-        ">": "&gt;",
-        "&": "&amp;",
-    ]
-    func htmlEscape(_ string: String) -> String {
-        var newString = ""
-        newString.reserveCapacity(string.count)
-        for c in string {
-            if let replacement = Self.htmlEscapedCharacters[c] {
-                newString += replacement
-            } else {
-                newString.append(c)
-            }
-        }
-        return newString
-    }
 }
 
diff --git a/Tests/HummingbirdMustacheTests/TemplateRendererTests.swift b/Tests/HummingbirdMustacheTests/TemplateRendererTests.swift
index 360f8a9..e18d651 100644
--- a/Tests/HummingbirdMustacheTests/TemplateRendererTests.swift
+++ b/Tests/HummingbirdMustacheTests/TemplateRendererTests.swift
@@ -166,7 +166,7 @@ final class TemplateRendererTests: XCTestCase {
         func wrapped(object: Any, template: HBMustacheTemplate) -> String {
             return "<b>\(template.render(object))</b>"
         }
-        let object: [String: Any] = ["name": "Willy", "wrapped": wrapped]
+        let object: [String: Any] = ["name": "Willy", "wrapped": HBMustacheLambda(wrapped)]
         XCTAssertEqual(template.render(object), """
             <b>Willy is awesome.</b>
             """)