diff --git a/Sources/HummingbirdMustache/CustomRenderable.swift b/Sources/HummingbirdMustache/CustomRenderable.swift
index b409f9b..307360b 100644
--- a/Sources/HummingbirdMustache/CustomRenderable.swift
+++ b/Sources/HummingbirdMustache/CustomRenderable.swift
@@ -14,16 +14,24 @@
 
 import Foundation
 
+/// Allow object to override standard hummingbird type rendering which uses
+/// `String(describing)`.
 public protocol HBMustacheCustomRenderable {
+    /// Custom rendered version of object
     var renderText: String { get }
+    /// Whether the object is a null object. Used when scoping sections
     var isNull: Bool { get }
 }
 
 extension HBMustacheCustomRenderable {
+    /// default version returning the standard rendering
     var renderText: String { String(describing: self) }
+    /// default version returning false
     var isNull: Bool { false }
 }
 
+/// Extend NSNull to conform to `HBMustacheCustomRenderable` to avoid outputting `<null>` and returning
+/// a valid response for `isNull`
 extension NSNull: HBMustacheCustomRenderable {
     public var renderText: String { "" }
     public var isNull: Bool { true }