Document EExtensible and EExtension.

The mechanism here is simple but hard to explain without leaning heavily
on object-oriented jargon.  Consider this a rough draft.  Illustrations
would certainly help clarify.

3 files changed, 86 insertions, 0 deletions

diff --git a/e-util/e-extensible.c b/e-util/e-extensible.c
index 9960d31d9f..a5e87c4280 100644
--- a/e-util/e-extensible.c
+++ b/e-util/e-extensible.c
@@ -16,6 +16,46 @@
  *
  */
 
+/**
+ * SECTION: e-extensible
+ * @short_description: an interface for extending objects
+ * @include: e-util/e-extensible.h
+ *
+ * #EExtension objects can be tacked on to any #GObject instance that
+ * implements the #EExtensible interface.  A #GObject type can be made
+ * extensible in two steps:
+ *
+ * 1. Add the #EExtensible interface when registering the #GType.
+ *    There are no methods to implement.
+ *
+ * <informalexample>
+ * <programlisting>
+ * #include <e-util/e-extensible.h>
+ *
+ * G_DEFINE_TYPE_WITH_CODE (
+ *         ECustomWidget, e_custom_widget, GTK_TYPE_WIDGET,
+ *         G_IMPLEMENT_INTERFACE (E_TYPE_EXTENSIBLE, NULL))
+ * </programlisting>
+ * </informalexample>
+ *
+ * 2. Load extensions for the class at some point during #GObject
+ *    initialization.  Generally this should be done toward the end of
+ *    the initialization code, so extensions get a fully initialized
+ *    object to work with.
+ *
+ * <informalexample>
+ * <programlisting>
+ * static void
+ * e_custom_widget_init (ECustomWidget *widget)
+ * {
+ *         Initialization code goes here...
+ *
+ *         e_extensible_load_extensions (E_EXTENSIBLE (widget));
+ * }
+ * </programlisting>
+ * </informalexample>
+ **/
+
 #include "e-extensible.h"
 
 #include <e-util/e-util.h>
@@ -89,6 +129,15 @@ e_extensible_get_type (void)
 	return type;
 }
 
+/**
+ * e_extensible_load_extensions:
+ * @extensible: an #EExtensible
+ *
+ * Creates an instance of all registered subtypes of #EExtension which
+ * target the class of @extensible.  The lifetimes of these newly created
+ * #EExtension objects are bound to @extensible such that they are finalized
+ * when @extensible is finalized.
+ **/
 void
 e_extensible_load_extensions (EExtensible *extensible)
 {
diff --git a/e-util/e-extension.c b/e-util/e-extension.c
index 05687b64ba..59eab840c9 100644
--- a/e-util/e-extension.c
+++ b/e-util/e-extension.c
@@ -16,6 +16,29 @@
  *
  */
 
+/**
+ * SECTION: e-extension
+ * @short_description: abstract base class for extensions
+ * @include: e-util/e-extension.h
+ *
+ * #EExtension provides a way to extend the functionality of objects
+ * that implement the #EExtensible interface.  #EExtension subclasses
+ * can target a particular extensible object type.  New instances of
+ * an extensible object type get paired with a new instance of each
+ * #EExtension subclass that targets the extensible object type.
+ *
+ * The first steps of writing a new extension are as follows:
+ *
+ * 1. Subclass #EExtension.
+ *
+ * 2. In the class initialization function, specify the #GType being
+ *    extended.  The #GType must implement the #EExtensible interface.
+ *
+ * 3. Register the extension's own #GType.  If the extension is to
+ *    be loaded dynamically using #GTypeModule, the type should be
+ *    registered in the library module's e_module_load() function.
+ **/
+
 #include "e-extension.h"
 
 #define E_EXTENSION_GET_PRIVATE(obj) \
@@ -151,6 +174,14 @@ e_extension_init (EExtension *extension)
 	extension->priv = E_EXTENSION_GET_PRIVATE (extension);
 }
 
+/**
+ * e_extension_get_extensible:
+ * @extension: an #EExtension
+ *
+ * Returns the object that @extension extends.
+ *
+ * Returns: the object being extended
+ **/
 EExtensible *
 e_extension_get_extensible (EExtension *extension)
 {
diff --git a/e-util/e-extension.h b/e-util/e-extension.h
index 905ef412f3..e9eee64a62 100644
--- a/e-util/e-extension.h
+++ b/e-util/e-extension.h
@@ -47,6 +47,12 @@ typedef struct _EExtension EExtension;
 typedef struct _EExtensionClass EExtensionClass;
 typedef struct _EExtensionPrivate EExtensionPrivate;
 
+/**
+ * EExtension:
+ *
+ * Contains only private data that should be read and manipulated using the
+ * functions below.
+ **/
 struct _EExtension {
 	GObject parent;
 	EExtensionPrivate *priv;