XML comments and tags in GObject documentation
Submitted by Michael Catanzaro
From the documentation for G_DEFINE_TYPE_WITH_PRIVATE: 
"A convenience macro for type implementations, which declares a class initialization function, an instance initialization function (see GTypeInfo for information about these), a static variable named t_n _parent_class pointing to the parent class, and adds private instance data to the type. Furthermore, it defines a *_get_type() function. See G_DEFINE_TYPE_EXTENDED() for an example.
Note that private structs added with this macros must have a struct name of the form
A quick search on just that page shows another comment in the description of G_DEFINE_TYPE and one in the description of GTypeClassCacheFunc, and one more use of
<replaceable> in the description of G_ADD_PRIVATE.