diff --git a/libgimp/gimpchannel.c b/libgimp/gimpchannel.c
index 6bb657b5eb..c44da9bfe1 100644
--- a/libgimp/gimpchannel.c
+++ b/libgimp/gimpchannel.c
@@ -66,6 +66,8 @@ gimp_channel_init (GimpChannel *channel)
  *
  * Returns: (transfer none): The newly created channel.
  *          The object belongs to libgimp and you should not free it.
+ *
+ * Since: 3.0
  */
 GimpChannel *
 gimp_channel_new (GimpImage     *image,
diff --git a/libgimp/gimpdisplay.c b/libgimp/gimpdisplay.c
index b66067c783..a44c4c9858 100644
--- a/libgimp/gimpdisplay.c
+++ b/libgimp/gimpdisplay.c
@@ -188,7 +188,7 @@ gimp_display_get_by_id (gint32 display_id)
  *
  * Returns: Whether the display is valid.
  *
- * Since: 2.4
+ * Since: 3.0
  **/
 gboolean
 gimp_display_is_valid (GimpDisplay *display)
diff --git a/libgimp/gimpdrawable.c b/libgimp/gimpdrawable.c
index c5146c14fa..51e936216a 100644
--- a/libgimp/gimpdrawable.c
+++ b/libgimp/gimpdrawable.c
@@ -64,6 +64,8 @@ gimp_drawable_init (GimpDrawable *drawable)
  *
  * Returns: (transfer full) (nullable): thumbnail data or %NULL if
  *          @drawable is invalid.
+ *
+ * Since: 3.0
  **/
 guchar *
 gimp_drawable_get_thumbnail_data (GimpDrawable *drawable,
@@ -104,7 +106,7 @@ gimp_drawable_get_thumbnail_data (GimpDrawable *drawable,
  *
  * Returns: (transfer full): a new #GdkPixbuf
  *
- * Since: 2.2
+ * Since: 3.0
  **/
 GdkPixbuf *
 gimp_drawable_get_thumbnail (GimpDrawable           *drawable,
@@ -133,6 +135,25 @@ gimp_drawable_get_thumbnail (GimpDrawable           *drawable,
   return NULL;
 }
 
+/**
+ * gimp_drawable_get_sub_thumbnail_data:
+ * @drawable:             the drawable ID
+ * @src_x:                the x coordinate of the area
+ * @src_y:                the y coordinate of the area
+ * @src_width:            the width of the area
+ * @src_height:           the height of the area
+ * @dest_width: (inout):  the requested thumbnail width  (<= 1024 pixels)
+ * @dest_height: (inout): the requested thumbnail height (<= 1024 pixels)
+ * @bpp: (out):           the bytes per pixel of the returned thumbnail data
+ *
+ * Retrieves thumbnail data for the drawable identified by @drawable.
+ * The thumbnail will be not larger than the requested size.
+ *
+ * Returns: (transfer full) (nullable): thumbnail data or %NULL if
+ *          @drawable is invalid.
+ *
+ * Since: 3.0
+ **/
 guchar *
 gimp_drawable_get_sub_thumbnail_data (GimpDrawable *drawable,
                                       gint          src_x,
@@ -182,7 +203,7 @@ gimp_drawable_get_sub_thumbnail_data (GimpDrawable *drawable,
  *
  * Returns: (transfer full): a new #GdkPixbuf
  *
- * Since: 2.2
+ * Since: 3.0
  **/
 GdkPixbuf *
 gimp_drawable_get_sub_thumbnail (GimpDrawable           *drawable,
@@ -234,7 +255,7 @@ gimp_drawable_get_sub_thumbnail (GimpDrawable           *drawable,
  *
  * See Also: gimp_drawable_get_shadow_buffer()
  *
- * Since: 2.10
+ * Since: 3.0
  */
 GeglBuffer *
 gimp_drawable_get_buffer (GimpDrawable *drawable)
@@ -267,7 +288,7 @@ gimp_drawable_get_buffer (GimpDrawable *drawable)
  *
  * See Also: gimp_drawable_get_shadow_buffer()
  *
- * Since: 2.10
+ * Since: 3.0
  */
 GeglBuffer *
 gimp_drawable_get_shadow_buffer (GimpDrawable *drawable)
@@ -295,7 +316,7 @@ gimp_drawable_get_shadow_buffer (GimpDrawable *drawable)
  *
  * Returns: The #Babl format.
  *
- * Since: 2.10
+ * Since: 3.0
  */
 const Babl *
 gimp_drawable_get_format (GimpDrawable *drawable)
@@ -373,6 +394,7 @@ gimp_drawable_get_format (GimpDrawable *drawable)
 
   return format;
 }
+
 /**
  * gimp_drawable_get_thumbnail_format:
  * @drawable: the ID of the #GimpDrawable to get the thumbnail format for.
@@ -381,7 +403,7 @@ gimp_drawable_get_format (GimpDrawable *drawable)
  *
  * Returns: The #Babl thumbnail format.
  *
- * Since: 2.10.14
+ * Since: 3.0
  */
 const Babl *
 gimp_drawable_get_thumbnail_format (GimpDrawable *drawable)
diff --git a/libgimp/gimpimage.c b/libgimp/gimpimage.c
index 5d26e57f0d..2ae9b2ba43 100644
--- a/libgimp/gimpimage.c
+++ b/libgimp/gimpimage.c
@@ -186,7 +186,7 @@ gimp_image_get_by_id (gint32 image_id)
  *
  * Returns: Whether the image is valid.
  *
- * Since: 2.4
+ * Since: 3.0
  **/
 gboolean
 gimp_image_is_valid (GimpImage *image)
@@ -275,6 +275,8 @@ gimp_list_images (void)
  *          The list of layers contained in the image.
  *          The returned array must be freed with g_free(). Layer
  *          elements belong to libgimp and must not be freed.
+ *
+ * Since: 3.0
  **/
 GimpLayer **
 gimp_image_get_layers (GimpImage *image,
@@ -313,6 +315,8 @@ gimp_image_get_layers (GimpImage *image,
  *          The list of channels contained in the image.
  *          The returned array must be freed with g_free(). Channel
  *          elements belong to libgimp and must not be freed.
+ *
+ * Since: 3.0
  **/
 GimpChannel **
 gimp_image_get_channels (GimpImage *image,
@@ -348,6 +352,8 @@ gimp_image_get_channels (GimpImage *image,
  *          The list of vectors contained in the image.
  *          The returned array must be freed with g_free(). Vectors
  *          elements belong to libgimp and must not be freed.
+ *
+ * Since: 3.0
  **/
 GimpVectors **
 gimp_image_get_vectors (GimpImage *image,
@@ -489,6 +495,8 @@ gimp_image_list_vectors (GimpImage *image)
  * is not of base type INDEXED, this pointer will be NULL.
  *
  * Returns: The image's colormap.
+ *
+ * Since: 3.0
  */
 guchar *
 gimp_image_get_colormap (GimpImage *image,
@@ -519,6 +527,8 @@ gimp_image_get_colormap (GimpImage *image,
  * in the "cmap" array.
  *
  * Returns: TRUE on success.
+ *
+ * Since: 3.0
  */
 gboolean
 gimp_image_set_colormap (GimpImage    *image,
@@ -543,6 +553,8 @@ gimp_image_set_colormap (GimpImage    *image,
  * gives the number of bytes per pixel in the image.
  *
  * Returns: (transfer full): the thumbnail data.
+ *
+ * Since: 3.0
  **/
 guchar *
 gimp_image_get_thumbnail_data (GimpImage *image,
@@ -582,7 +594,7 @@ gimp_image_get_thumbnail_data (GimpImage *image,
  *
  * Returns: (transfer full): a new #GdkPixbuf
  *
- * Since: 2.2
+ * Since: 3.0
  **/
 GdkPixbuf *
 gimp_image_get_thumbnail (GimpImage              *image,
@@ -621,7 +633,7 @@ gimp_image_get_thumbnail (GimpImage              *image,
  * Returns: (nullable) (transfer full): The exif/ptc/xmp metadata,
  *          or %NULL if there is none.
  *
- * Since: 2.10
+ * Since: 3.0
  **/
 GimpMetadata *
 gimp_image_get_metadata (GimpImage *image)
@@ -651,7 +663,7 @@ gimp_image_get_metadata (GimpImage *image)
  *
  * Returns: TRUE on success.
  *
- * Since: 2.10
+ * Since: 3.0
  **/
 gboolean
 gimp_image_set_metadata (GimpImage    *image,
diff --git a/libgimp/gimpitem.c b/libgimp/gimpitem.c
index acdc8cb2ca..ac507f8dbd 100644
--- a/libgimp/gimpitem.c
+++ b/libgimp/gimpitem.c
@@ -218,7 +218,7 @@ gimp_item_get_by_id (gint32 item_id)
  *
  * Returns: Whether the item is valid.
  *
- * Since: 2.8
+ * Since: 3.0
  **/
 gboolean
 gimp_item_is_valid (GimpItem *item)
@@ -236,7 +236,7 @@ gimp_item_is_valid (GimpItem *item)
  *
  * Returns: TRUE if the item is a drawable, FALSE otherwise.
  *
- * Since: 2.8
+ * Since: 3.0
  **/
 gboolean
 gimp_item_is_drawable (GimpItem *item)
@@ -254,7 +254,7 @@ gimp_item_is_drawable (GimpItem *item)
  *
  * Returns: TRUE if the item is a layer, FALSE otherwise.
  *
- * Since: 2.8
+ * Since: 3.0
  **/
 gboolean
 gimp_item_is_layer (GimpItem *item)
@@ -273,7 +273,7 @@ gimp_item_is_layer (GimpItem *item)
  *
  * Returns: TRUE if the item is a text layer, FALSE otherwise.
  *
- * Since: 2.8
+ * Since: 3.0
  **/
 gboolean
 gimp_item_is_text_layer (GimpItem *item)
@@ -291,7 +291,7 @@ gimp_item_is_text_layer (GimpItem *item)
  *
  * Returns: TRUE if the item is a channel, FALSE otherwise.
  *
- * Since: 2.8
+ * Since: 3.0
  **/
 gboolean
 gimp_item_is_channel (GimpItem *item)
@@ -310,7 +310,7 @@ gimp_item_is_channel (GimpItem *item)
  *
  * Returns: TRUE if the item is a layer mask, FALSE otherwise.
  *
- * Since: 2.8
+ * Since: 3.0
  **/
 gboolean
 gimp_item_is_layer_mask (GimpItem *item)
@@ -328,7 +328,7 @@ gimp_item_is_layer_mask (GimpItem *item)
  *
  * Returns: TRUE if the item is a selection, FALSE otherwise.
  *
- * Since: 2.8
+ * Since: 3.0
  **/
 gboolean
 gimp_item_is_selection (GimpItem *item)
@@ -346,7 +346,7 @@ gimp_item_is_selection (GimpItem *item)
  *
  * Returns: TRUE if the item is a vectors, FALSE otherwise.
  *
- * Since: 2.8
+ * Since: 3.0
  **/
 gboolean
 gimp_item_is_vectors (GimpItem *item)
@@ -368,6 +368,8 @@ gimp_item_is_vectors (GimpItem *item)
  *          The item's list of children.
  *          The returned array must be freed with g_free(). Item
  *          elements belong to libgimp and must not be unrefed.
+ *
+ * Since: 3.0
  **/
 GimpItem **
 gimp_item_get_children (GimpItem *item,
diff --git a/libgimp/gimplayer.c b/libgimp/gimplayer.c
index 677df53587..6fcc394e0b 100644
--- a/libgimp/gimplayer.c
+++ b/libgimp/gimplayer.c
@@ -136,7 +136,7 @@ gimp_layer_copy (GimpLayer *layer)
  * Returns: (transfer none): The newly created layer.
  *          The object belongs to libgimp and you should not free it.
  *
- * Since: 2.2
+ * Since: 3.0
  */
 GimpLayer *
 gimp_layer_new_from_pixbuf (GimpImage     *image,
@@ -215,14 +215,14 @@ gimp_layer_new_from_pixbuf (GimpImage     *image,
  * Returns: (transfer none): The newly created layer.
  *          The object belongs to libgimp and you should not free it.
  *
- * Since: 2.8
+ * Since: 3.0
  */
 GimpLayer *
-gimp_layer_new_from_surface (GimpImage            *image,
-                             const gchar          *name,
-                             cairo_surface_t      *surface,
-                             gdouble               progress_start,
-                             gdouble               progress_end)
+gimp_layer_new_from_surface (GimpImage       *image,
+                             const gchar     *name,
+                             cairo_surface_t *surface,
+                             gdouble          progress_start,
+                             gdouble          progress_end)
 {
   GeglBuffer    *src_buffer;
   GeglBuffer    *dest_buffer;
@@ -278,7 +278,7 @@ gimp_layer_new_from_surface (GimpImage            *image,
 }
 
 
-/* Deprecate API. */
+/* Deprecated API. */
 
 
 /**
diff --git a/libgimp/gimpselection.c b/libgimp/gimpselection.c
index e4a8aa7176..697730b8dd 100644
--- a/libgimp/gimpselection.c
+++ b/libgimp/gimpselection.c
@@ -62,6 +62,8 @@ gimp_selection_init (GimpSelection *selection)
  * positioning of the new floating selection.
  *
  * Returns: (transfer none): The floated layer.
+ *
+ * Since: 3.0
  */
 GimpLayer *
 gimp_selection_float (GimpImage    *image,