docs: don't use <para id="">

gdk/gdkkeys.c

@@ -57,7 +57,8 @@
  * When it makes sense, key values can be converted to and from
  * Unicode characters with gdk_keyval_to_unicode() and gdk_unicode_to_keyval().
  *
- * <para id="key-group-explanation">
+ * # Groups # {#key-group-explanation}
+ *
  * One #GdkKeymap object exists for each user display. gdk_keymap_get_default()
  * returns the #GdkKeymap for the default display; to obtain keymaps for other
  * displays, use gdk_keymap_get_for_display(). A keymap
@@ -78,7 +79,6 @@
  * group 0, a key might have two English characters, and in group 1 it might have
  * two Hebrew characters. The Hebrew characters will be printed on the key next to
  * the English characters.
- * </para>
  *
  * In order to use a keymap to interpret a key event, it's necessary to first
  * convert the keyboard state into an effective group and level. This is done via a

gdk/gdkwindow.c

@@ -60,20 +60,20 @@
  * and so on; a #GtkWindow may contain many #GdkWindows. For example,
  * each #GtkButton has a #GdkWindow associated with it.
  *
- * ## Composited Windows
+ * # Composited Windows # {#COMPOSITED-WINDOWS}
  *
- * <para id="COMPOSITED-WINDOWS">Normally, the windowing system takes care of rendering the contents
+ * Normally, the windowing system takes care of rendering the contents
  * of a child window onto its parent window. This mechanism can be
  * intercepted by calling gdk_window_set_composited() on the child
  * window. For a “composited” window it is the
  * responsibility of the application to render the window contents at
- * the right spot.</para>
+ * the right spot.
  *
- * ## Offscreen Windows
+ * # Offscreen Windows # {#OFFSCREEN-WINDOWS}
  *
- * <para id="OFFSCREEN-WINDOWS">Offscreen windows are more general than composited windows, since
+ * Offscreen windows are more general than composited windows, since
  * they allow not only to modify the rendering of the child window onto
- * its parent, but also to apply coordinate transformations.</para>
+ * its parent, but also to apply coordinate transformations.
  *
  * To integrate an offscreen window into a window hierarchy, one has
  * to call gdk_offscreen_window_set_embedder() and handle a number of