app: Add some comments on classes used for the dock system

app/widgets/gimpdock.h

@@ -36,6 +36,9 @@
 typedef struct _GimpDockClass GimpDockClass;
 typedef struct _GimpDockPriv  GimpDockPriv;
 
+/**
+ * A top-level window containing GimpDockbooks.
+ */
 struct _GimpDock
 {
   GimpWindow    parent_instance;

app/widgets/gimpdockable.h

@@ -35,6 +35,11 @@
 
 typedef struct _GimpDockableClass GimpDockableClass;
 
+/**
+ * A kind of adpater to make other widgets dockable. The widget to
+ * dock is put inside the GimpDockable, which is put in a
+ * GimpDockbook.
+ */
 struct _GimpDockable
 {
   GtkBin        parent_instance;

app/widgets/gimpdockbook.h

@@ -32,6 +32,10 @@
 
 typedef struct _GimpDockbookClass  GimpDockbookClass;
 
+/**
+ * Holds GimpDockables which are presented on different tabs using
+ * GtkNotebook.
+ */
 struct _GimpDockbook
 {
   GtkNotebook    parent_instance;

app/widgets/gimpdocked.h

@@ -30,6 +30,9 @@
 
 typedef struct _GimpDockedInterface GimpDockedInterface;
 
+/**
+ * Interface with common methods for stuff that is docked.
+ */
 struct _GimpDockedInterface
 {
   GTypeInterface base_iface;

app/widgets/gimpdockseparator.h

@@ -32,6 +32,10 @@
 
 typedef struct _GimpDockSeparatorClass GimpDockSeparatorClass;
 
+/**
+ * Separates dockable and acts as drop-targets to allow rearrangements
+ * of them.
+ */
 struct _GimpDockSeparator
 {
   GtkEventBox    parent_instance;

app/widgets/gimpimagedock.h

@@ -35,6 +35,9 @@
 
 typedef struct _GimpImageDockClass   GimpImageDockClass;
 
+/**
+ * Adds some GimpImage specific hooks and logic to GimpDock.
+ */
 struct _GimpImageDock
 {
   GimpDock       parent_instance;