+There are several predefined GType values that correspond to fundamental or base types.
+@begin{itemize}
+@item{@variable{+g-type-invalid+}}
+@item{@variable{+g-type-void+}}
+@item{@variable{+g-type-interface+}}
+@item{@variable{+g-type-char+}}
+@item{@variable{+g-type-uchar+}}
+@item{@variable{+g-type-boolean+}}
+@item{@variable{+g-type-int+}}
+@item{@variable{+g-type-uint+}}
+@item{@variable{+g-type-long+}}
+@item{@variable{+g-type-ulong+}}
+@item{@variable{+g-type-int64+}}
+@item{@variable{+g-type-uint64+}}
+@item{@variable{+g-type-enum+}}
+@item{@variable{+g-type-flags+}}
+@item{@variable{+g-type-float+}}
+@item{@variable{+g-type-double+}}
+@item{@variable{+g-type-string+}}
+@item{@variable{+g-type-pointer+}}
+@item{@variable{+g-type-boxed+}}
+@item{@variable{+g-type-param+}}
+@item{@variable{+g-type-object+}}
+@end{itemize}
+
+GType values form type hierarchies via signle inheritance. Functions @fun{g-type-parent} and @fun{g-type-children} enable to traverse through the type hierarchy.
+
+For some types, additional information is available. Functions @fun{class-properties} and @fun{interface-properties} return properties of classes and interfaces. Functions @fun{get-enum-items} and @fun{get-flags-items} return members of enum and flags types.
+
+//TODO: document and refactor signals
+
+@end{section}
+
+@begin[GValue]{section}
+GObject uses GValues as a generic way to pass values. It is used when calling closures, emitting signals, setting and getting properties' values, passing values to object constructors. @class{g-value} foreign structure is used for holding GValue. It used like all foreign structures: either with @code{cffi:foreign-alloc} or with @code{cffi:with-foreign-object}. Before first use, @class{g-value} should be zeroed with @fun{g-value-zero}. Zeroed @class{g-value} may be configured to hold a GValue of a given type with @fun{g-value-init}. @fun{parse-g-value} retrieves the Lisp object corresponding to the value stored in GValue. @fun{set-g-value} sets the GValue from Lisp object.
+@end{section}"))
+
+(in-package :gobject)