diff --git a/libgimp/gimplegacy.h b/libgimp/gimplegacy.h
index 4c5e20b748..d880185c2e 100644
--- a/libgimp/gimplegacy.h
+++ b/libgimp/gimplegacy.h
@@ -88,6 +88,12 @@ struct _GimpPlugInInfo
   GimpRunProc   run_proc;
 };
 
+/**
+ * GimpParamDef:
+ * @type:        the parameter's type.
+ * @name:        the parameter's name.
+ * @description: the parameter's desctiption.
+ **/
 struct _GimpParamDef
 {
   GimpPDBArgType  type;
@@ -95,6 +101,34 @@ struct _GimpParamDef
   gchar          *description;
 };
 
+/**
+ * GimpParamData:
+ * @d_int32:       a 32-bit integer.
+ * @d_int16:       a 16-bit integer.
+ * @d_int8:        an 8-bit unsigned integer.
+ * @d_float:       a double.
+ * @d_string:      a string.
+ * @d_color:       a #GimpRGB.
+ * @d_int32array:  an array of int32.
+ * @d_int16array:  an array of int16.
+ * @d_int8array:   an array of int8.
+ * @d_floatarray:  an array of floats.
+ * @d_stringarray: an array of strings.
+ * @d_colorarray:  an array of colors.
+ * @d_display:     a display id.
+ * @d_image:       an image id.
+ * @d_item:        an item id.
+ * @d_drawable:    a drawable id.
+ * @d_layer:       a layer id.
+ * @d_channel:     a channel id.
+ * @d_layer_mask:  a layer mask id.
+ * @d_selection:   a selection id.
+ * @d_vectors:     a vectors id.
+ * @d_unit:        a GimpUnit.
+ * @d_parasite:    a GimpParasite.
+ * @d_tattoo:      a tattoo.
+ * @d_status:      a return status.
+ **/
 union _GimpParamData
 {
   gint32            d_int32;
@@ -102,22 +136,21 @@ union _GimpParamData
   guint8            d_int8;
   gdouble           d_float;
   gchar            *d_string;
+  GimpRGB           d_color;
   gint32           *d_int32array;
   gint16           *d_int16array;
   guint8           *d_int8array;
   gdouble          *d_floatarray;
   gchar           **d_stringarray;
   GimpRGB          *d_colorarray;
-  GimpRGB           d_color;
   gint32            d_display;
   gint32            d_image;
   gint32            d_item;
-  gint32            d_layer;
-  gint32            d_layer_mask;
-  gint32            d_channel;
   gint32            d_drawable;
+  gint32            d_layer;
+  gint32            d_channel;
+  gint32            d_layer_mask;
   gint32            d_selection;
-  gint32            d_boundary;
   gint32            d_vectors;
   gint32            d_unit;
   GimpParasite      d_parasite;
@@ -125,6 +158,11 @@ union _GimpParamData
   GimpPDBStatusType d_status;
 };
 
+/**
+ * GimpParam:
+ * @type: the parameter's type.
+ * @data: the parameter's data.
+ **/
 struct _GimpParam
 {
   GimpPDBArgType type;
diff --git a/libgimp/gimploadprocedure.c b/libgimp/gimploadprocedure.c
index a0f4a0d155..487244138e 100644
--- a/libgimp/gimploadprocedure.c
+++ b/libgimp/gimploadprocedure.c
@@ -225,7 +225,11 @@ gimp_load_procedure_run (GimpProcedure        *procedure,
  *
  * (run-mode, uri, raw-uri)
  *
- * arguments of a load procedure. It is possible to add additional
+ * arguments and the standard
+ *
+ * (image-id)
+ *
+ * return value of a load procedure. It is possible to add additional
  * arguments.
  *
  * When invoked via gimp_procedure_run(), it unpacks these standard
@@ -332,7 +336,7 @@ gimp_load_procedure_set_thumbnail_loader (GimpLoadProcedure *procedure,
  * @procedure: A #GimpLoadProcedure.
  *
  * Returns: The procedure's thumbnail loader procedure as set with
- *          gimp_load_procedure_set_thumbnail_procedure().
+ *          gimp_load_procedure_set_thumbnail_loader().
  *
  * Since: 3.0
  **/
diff --git a/libgimp/gimpprogress.c b/libgimp/gimpprogress.c
index dfdbe35d40..20dcc5646a 100644
--- a/libgimp/gimpprogress.c
+++ b/libgimp/gimpprogress.c
@@ -64,8 +64,10 @@ static const gdouble   gimp_progress_step    = (1.0 / 256.0);
 
 /**
  * gimp_progress_install_vtable:
- * @vtable:    a pointer to a @GimpProgressVtable.
- * @user_data: a pointer that is passed as user_data to all vtable functions.
+ * @vtable:            a pointer to a @GimpProgressVtable.
+ * @user_data:         a pointer that is passed as user_data to all vtable
+ *                     functions.
+ * @user_data_destroy: (nullable): destroy function for @user_data, or %NULL.
  *
  * Returns: the name of the temporary procedure that's been installed
  *
diff --git a/libgimp/gimpprogress.h b/libgimp/gimpprogress.h
index 5d608d3f27..fdbb2089ed 100644
--- a/libgimp/gimpprogress.h
+++ b/libgimp/gimpprogress.h
@@ -30,6 +30,23 @@ G_BEGIN_DECLS
 
 typedef struct _GimpProgressVtable GimpProgressVtable;
 
+/**
+ * GimpProgressVtable:
+ * @start:      starts the progress.
+ * @end:        ends the progress.
+ * @set_text:   sets a new text on the progress.
+ * @set_value:  sets a new percentage on the progress.
+ * @pulse:      makes the progress pulse.
+ * @get_window: returns the ID of the window where the progress is displayed.
+ * @_gimp_reserved1: reserved pointer for future expansion.
+ * @_gimp_reserved2: reserved pointer for future expansion.
+ * @_gimp_reserved3: reserved pointer for future expansion.
+ * @_gimp_reserved4: reserved pointer for future expansion.
+ * @_gimp_reserved5: reserved pointer for future expansion.
+ * @_gimp_reserved6: reserved pointer for future expansion.
+ * @_gimp_reserved7: reserved pointer for future expansion.
+ * @_gimp_reserved8: reserved pointer for future expansion.
+ **/
 struct _GimpProgressVtable
 {
   void    (* start)        (const gchar *message,