diff --git a/src/Arduboy2.h b/src/Arduboy2.h
index 41724f1..77b88b4 100644
--- a/src/Arduboy2.h
+++ b/src/Arduboy2.h
@@ -117,7 +117,7 @@ struct Point
  * _minus_ text output.
  *
  * This class in inherited by Arduboy2, so if text output functions are
- * requred Arduboy2 should be used instead.
+ * required Arduboy2 should be used instead.
  *
  * \note
  * \parblock
@@ -139,10 +139,20 @@ struct Point
  * \endcode
  * \endparblock
  *
+ * \note
+ * \parblock
+ * A friend class named _Arduboy2Ex_ is declared by this class. The intention
+ * is to allow a sketch to create an _Arduboy2Ex_ class which would have access
+ * to the private and protected members of the Arduboy2Base class. It is hoped
+ * that this may eliminate the need to create an entire local copy of the
+ * library, in order to extend the functionality, in most circumstances.
+ * \endparblock
+ *
  * \see Arduboy2
  */
 class Arduboy2Base : public Arduboy2Core
 {
+ friend class Arduboy2Ex;
  friend class Sprites;
 
  public:
@@ -819,10 +829,19 @@ class Arduboy2Base : public Arduboy2Core
  * This class is derived from Arduboy2Base. It provides text output functions
  * in addition to all the functions inherited from Arduboy2Base.
  *
+ * \note
+ * A friend class named _Arduboy2Ex_ is declared by this class. The intention
+ * is to allow a sketch to create an _Arduboy2Ex_ class which would have access
+ * to the private and protected members of the Arduboy2 class. It is hoped
+ * that this may eliminate the need to create an entire local copy of the
+ * library, in order to extend the functionality, in most circumstances.
+ *
  * \see Arduboy2Base
  */
 class Arduboy2 : public Print, public Arduboy2Base
 {
+ friend class Arduboy2Ex;
+
  public:
   Arduboy2();
 
diff --git a/src/Arduboy2Audio.h b/src/Arduboy2Audio.h
index fea5fc8..afa6e54 100644
--- a/src/Arduboy2Audio.h
+++ b/src/Arduboy2Audio.h
@@ -60,9 +60,20 @@
  * ArduboyTones sound(arduboy.audio.enabled);
  * \endcode
  * \endparblock
+ *
+ * \note
+ * \parblock
+ * A friend class named _Arduboy2Ex_ is declared by this class. The intention
+ * is to allow a sketch to create an _Arduboy2Ex_ class which would have access
+ * to the private and protected members of the Arduboy2Audio class. It is hoped
+ * that this may eliminate the need to create an entire local copy of the
+ * library, in order to extend the functionality, in most circumstances.
+ * \endparblock
  */
 class Arduboy2Audio
 {
+ friend class Arduboy2Ex;
+
  public:
   /** \brief
    * Initialize the speaker based on the current mute setting.
diff --git a/src/Arduboy2Core.h b/src/Arduboy2Core.h
index bb5182f..03d4062 100644
--- a/src/Arduboy2Core.h
+++ b/src/Arduboy2Core.h
@@ -145,9 +145,18 @@
  * \details
  * This class is inherited by Arduboy2Base and thus also Arduboy2, so wouldn't
  * normally be used directly by a sketch.
+ *
+ * \note
+ * A friend class named _Arduboy2Ex_ is declared by this class. The intention
+ * is to allow a sketch to create an _Arduboy2Ex_ class which would have access
+ * to the private and protected members of the Arduboy2Core class. It is hoped
+ * that this may eliminate the need to create an entire local copy of the
+ * library, in order to extend the functionality, in most circumstances.
  */
 class Arduboy2Core
 {
+  friend class Arduboy2Ex;
+
   public:
     Arduboy2Core();
 
@@ -422,18 +431,22 @@ class Arduboy2Core
      * to 255 (fully on).
      *
      * \note
+     * \parblock
      * Certain libraries that take control of the hardware timers may interfere
      * with the ability of this function to properly control the RGB LED.
      *_ArduboyPlaytune_ is one such library known to do this.
      * The digitalWriteRGB() function will still work properly in this case.
+     * \endparblock
      *
      * \note
+     * \parblock
      * Many of the Kickstarter Arduboys were accidentally shipped with the
      * RGB LED installed incorrectly. For these units, the green LED cannot be
      * lit. As long as the green led is set to off, setting the red LED will
      * actually control the blue LED and setting the blue LED will actually
      * control the red LED. If the green LED is turned fully on, none of the
      * LEDs will light.
+     * \endparblock
      *
      * \see digitalWriteRGB()
      */