diff --git a/src/hb-aat-layout.cc b/src/hb-aat-layout.cc
index 74ebaa64e..b0e809db0 100644
--- a/src/hb-aat-layout.cc
+++ b/src/hb-aat-layout.cc
@@ -227,7 +227,7 @@ hb_aat_layout_compile_map (const hb_aat_map_builder_t *mapper,
  *
  * <note>Note: does not examine the `GSUB` table.</note>
  *
- * Return value: true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 2.3.0
  */
@@ -294,7 +294,7 @@ hb_aat_layout_remove_deleted_glyphs (hb_buffer_t *buffer)
  *
  * <note>Note: does not examine the `GPOS` table.</note>
  *
- * Return value: true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 2.3.0
  */
@@ -325,7 +325,7 @@ hb_aat_layout_position (const hb_ot_shape_plan_t *plan,
  * Tests whether the specified face includes any tracking information
  * in the `trak` table.
  *
- * Return value: true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 2.3.0
  */
diff --git a/src/hb-blob.cc b/src/hb-blob.cc
index e340bc346..9c838e59c 100644
--- a/src/hb-blob.cc
+++ b/src/hb-blob.cc
@@ -299,7 +299,7 @@ hb_blob_make_immutable (hb_blob_t *blob)
  *
  * Tests whether a blob is immutable.
  *
- * Return value: %true if @blob is immutable, false otherwise
+ * Return value: %true if @blob is immutable, %false otherwise
  *
  * Since: 0.9.2
  **/
diff --git a/src/hb-common.cc b/src/hb-common.cc
index ddbcaa064..7615cc6d9 100644
--- a/src/hb-common.cc
+++ b/src/hb-common.cc
@@ -675,8 +675,8 @@ hb_version_string ()
  * Tests the library version against a minimum value,
  * as three integer components.
  *
- * Return value: True if the library is equal to or greater than
- * the test value, false otherwise
+ * Return value: %true if the library is equal to or greater than
+ * the test value, %false otherwise
  *
  * Since: 0.9.30
  **/
diff --git a/src/hb-face.cc b/src/hb-face.cc
index 33a788e7c..007aa71a3 100644
--- a/src/hb-face.cc
+++ b/src/hb-face.cc
@@ -360,7 +360,7 @@ hb_face_make_immutable (hb_face_t *face)
  *
  * Tests whether the given face object is immutable.
  *
- * Return value: True is @face is immutable, false otherwise
+ * Return value: %true is @face is immutable, %false otherwise
  *
  * Since: 0.9.2
  **/
diff --git a/src/hb-font.cc b/src/hb-font.cc
index 5c8357ff2..5d3b13187 100644
--- a/src/hb-font.cc
+++ b/src/hb-font.cc
@@ -690,7 +690,7 @@ hb_font_funcs_make_immutable (hb_font_funcs_t *ffuncs)
  *
  * Tests whether a font-functions structure is immutable.
  *
- * Return value: %true if @ffuncs is immutable, false otherwise
+ * Return value: %true if @ffuncs is immutable, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -756,7 +756,7 @@ hb_font_t::has_func (unsigned int i)
  * Fetches the extents for a specified font, in horizontal
  * text segments.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 1.1.3
  **/
@@ -775,7 +775,7 @@ hb_font_get_h_extents (hb_font_t         *font,
  * Fetches the extents for a specified font, in vertical
  * text segments.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 1.1.3
  **/
@@ -799,7 +799,7 @@ hb_font_get_v_extents (hb_font_t         *font,
  * If @variation_selector is 0, calls hb_font_get_nominal_glyph();
  * otherwise calls hb_font_get_variation_glyph().
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -827,7 +827,7 @@ hb_font_get_glyph (hb_font_t      *font,
  * for code points modified by variation selectors. For variation-selector
  * support, user hb_font_get_variation_glyph() or use hb_font_get_glyph().
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 1.2.3
  **/
@@ -873,7 +873,7 @@ hb_font_get_nominal_glyphs (hb_font_t *font,
  * by the specified variation-selector code point, in the specified
  * font.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 1.2.3
  **/
@@ -983,7 +983,7 @@ hb_font_get_glyph_v_advances (hb_font_t*            font,
  * Fetches the (X,Y) coordinates of the origin for a glyph ID
  * in the specified font, for horizontal text segments.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -1006,7 +1006,7 @@ hb_font_get_glyph_h_origin (hb_font_t      *font,
  * Fetches the (X,Y) coordinates of the origin for a glyph ID
  * in the specified font, for vertical text segments.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -1079,7 +1079,7 @@ hb_font_get_glyph_v_kerning (hb_font_t      *font,
  * Fetches the #hb_glyph_extents_t data for a glyph ID
  * in the specified font.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -1102,7 +1102,7 @@ hb_font_get_glyph_extents (hb_font_t          *font,
  * Fetches the (x,y) coordinates of a specified contour-point index
  * in the specified glyph, within the specified font.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -1125,7 +1125,7 @@ hb_font_get_glyph_contour_point (hb_font_t      *font,
  *
  * Fetches the glyph-name string for a glyph ID in the specified @font.
  *
- * Return value: %true if data found, zero otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -1149,7 +1149,7 @@ hb_font_get_glyph_name (hb_font_t      *font,
  *
  * <note>Note: @len == -1 means the name string is null-terminated.</note>
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -1364,7 +1364,7 @@ hb_font_get_glyph_kerning_for_direction (hb_font_t      *font,
  * Calls the appropriate direction-specific variant (horizontal
  * or vertical) depending on the value of @direction.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -1393,7 +1393,7 @@ hb_font_get_glyph_extents_for_origin (hb_font_t          *font,
  * Calls the appropriate direction-specific variant (horizontal
  * or vertical) depending on the value of @direction.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -1444,7 +1444,7 @@ hb_font_glyph_to_string (hb_font_t      *font,
  *
  * <note>Note: @len == -1 means the string is null-terminated.</note>
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -1728,7 +1728,7 @@ hb_font_make_immutable (hb_font_t *font)
  *
  * Tests whether a font object is immutable.
  *
- * Return value: %true if @font is immutable, false otherwise
+ * Return value: %true if @font is immutable, %false otherwise
  *
  * Since: 0.9.2
  **/
diff --git a/src/hb-map.cc b/src/hb-map.cc
index f898bd8f9..6447ade93 100644
--- a/src/hb-map.cc
+++ b/src/hb-map.cc
@@ -162,7 +162,7 @@ hb_map_get_user_data (hb_map_t           *map,
  *
  * Tests whether memory allocation for a set was successful.
  *
- * Return value: %true if allocation succeeded, false otherwise
+ * Return value: %true if allocation succeeded, %false otherwise
  *
  * Since: 1.7.7
  **/
@@ -230,7 +230,7 @@ hb_map_del (hb_map_t       *map,
  *
  * Tests whether @key is an element of @map.
  *
- * Return value: %true if @key is found in @map, false otherwise
+ * Return value: %true if @key is found in @map, %false otherwise
  *
  * Since: 1.7.7
  **/
diff --git a/src/hb-ot-color.cc b/src/hb-ot-color.cc
index 0e7203a88..fb8ed08d9 100644
--- a/src/hb-ot-color.cc
+++ b/src/hb-ot-color.cc
@@ -64,7 +64,7 @@
  *
  * Tests whether a face includes a `CPAL` color-palette table.
  *
- * Return value: true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 2.1.0
  */
@@ -195,7 +195,7 @@ hb_ot_color_palette_get_colors (hb_face_t     *face,
  *
  * Tests whether a face includes any `COLR` color layers.
  *
- * Return value: true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 2.1.0
  */
@@ -242,7 +242,7 @@ hb_ot_color_glyph_get_layers (hb_face_t           *face,
  *
  * Tests whether a face includes any `SVG` glyph images.
  *
- * Return value: true if data found, false otherwise.
+ * Return value: %true if data found, %false otherwise.
  *
  * Since: 2.1.0
  */
@@ -280,7 +280,7 @@ hb_ot_color_glyph_reference_svg (hb_face_t *face, hb_codepoint_t glyph)
  *
  * Tests whether a face has PNG glyph images (either in `CBDT` or `sbix` tables).
  *
- * Return value: true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 2.1.0
  */
diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 83d7f3e1e..91a56c552 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -76,7 +76,7 @@
  * Tests whether a face includes any kerning data in the 'kern' table.
  * Does NOT test for kerning lookups in the GPOS table.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  **/
 bool
@@ -92,7 +92,7 @@ hb_ot_layout_has_kerning (hb_face_t *face)
  * Tests whether a face includes any state-machine kerning in the 'kern' table.
  * Does NOT examine the GPOS table.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  **/
 bool
@@ -112,7 +112,7 @@ hb_ot_layout_has_machine_kerning (hb_face_t *face)
  *
  * Does NOT examine the GPOS table.
  *
- * Return value: %true is data found, false otherwise
+ * Return value: %true is data found, %false otherwise
  *
  **/
 bool
@@ -268,7 +268,7 @@ _hb_ot_layout_set_glyph_props (hb_font_t *font,
  *
  * Tests whether a face has any glyph classes defined in its GDEF table.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  **/
 hb_bool_t
@@ -444,7 +444,7 @@ hb_ot_layout_table_get_script_tags (hb_face_t    *face,
  * Fetches the index if a given script tag in the specified face's GSUB table
  * or GPOS table.
  *
- * Return value: %true if the script is found, false otherwise
+ * Return value: %true if the script is found, %false otherwise
  *
  **/
 hb_bool_t
@@ -598,7 +598,7 @@ hb_ot_layout_table_get_feature_tags (hb_face_t    *face,
  * Fetches the index for a given feature tag in the specified face's GSUB table
  * or GPOS table.
  *
- * Return value: %true if the feature is found, false otherwise
+ * Return value: %true if the feature is found, %false otherwise
  **/
 bool
 hb_ot_layout_table_find_feature (hb_face_t    *face,
@@ -663,7 +663,7 @@ hb_ot_layout_script_get_language_tags (hb_face_t    *face,
  * Fetches the index of a given language tag in the specified face's GSUB table
  * or GPOS table, underneath the specified script tag.
  *
- * Return value: %true if the language tag is found, false otherwise
+ * Return value: %true if the language tag is found, %false otherwise
  *
  * Since: ??
  * Deprecated: ??
@@ -697,7 +697,7 @@ hb_ot_layout_script_find_language (hb_face_t    *face,
  * Fetches the index of a given language tag in the specified face's GSUB table
  * or GPOS table, underneath the specified script index.
  *
- * Return value: %true if the language tag is found, false otherwise
+ * Return value: %true if the language tag is found, %false otherwise
  *
  * Since: 2.0.0
  **/
@@ -739,7 +739,7 @@ hb_ot_layout_script_select_language (hb_face_t      *face,
  * Fetches the index of a requested feature in the given face's GSUB or GPOS table,
  * underneath the specified script and language.
  *
- * Return value: %true if the feature is found, false otherwise
+ * Return value: %true if the feature is found, %false otherwise
  *
  **/
 hb_bool_t
@@ -770,7 +770,7 @@ hb_ot_layout_language_get_required_feature_index (hb_face_t    *face,
  * Fetches the tag of a requested feature index in the given face's GSUB or GPOS table,
  * underneath the specified script and language.
  *
- * Return value: %true if the feature is found, false otherwise
+ * Return value: %true if the feature is found, %false otherwise
  *
  * Since: 0.9.30
  **/
@@ -877,7 +877,7 @@ hb_ot_layout_language_get_feature_tags (hb_face_t    *face,
  * Fetches the index of a given feature tag in the specified face's GSUB table
  * or GPOS table, underneath the specified script and language.
  *
- * Return value: %true if the feature is found, false otherwise
+ * Return value: %true if the feature is found, %false otherwise
  *
  **/
 hb_bool_t
@@ -1310,7 +1310,7 @@ hb_ot_layout_feature_with_variations_get_lookups (hb_face_t    *face,
  *
  * Tests whether the specified face includes any GSUB substitutions.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  **/
 hb_bool_t
@@ -1331,7 +1331,7 @@ hb_ot_layout_has_substitution (hb_face_t *face)
  * Tests whether a specified lookup in the specified face would
  * trigger a substitution on the given glyph sequence.
  *
- * Return value: %true if a substitution would be triggered, false otherwise
+ * Return value: %true if a substitution would be triggered, %false otherwise
  *
  * Since: 0.9.7
  **/
@@ -1488,7 +1488,7 @@ hb_ot_layout_lookups_substitute_closure (hb_face_t      *face,
  * hb_ot_layout_has_positioning:
  * @face: #hb_face_t to work upon
  *
- * Return value: %true if the face has GPOS data, false otherwise
+ * Return value: %true if the face has GPOS data, %false otherwise
  *
  **/
 hb_bool_t
@@ -1561,7 +1561,7 @@ hb_ot_layout_position_finish_offsets (hb_font_t *font, hb_buffer_t *buffer)
  * For more information on this distinction, see the [`size` feature documentation](
  * https://docs.microsoft.com/en-us/typography/opentype/spec/features_pt#tag-size).
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 0.9.10
  **/
@@ -1625,7 +1625,7 @@ hb_ot_layout_get_size_params (hb_face_t       *face,
  * Fetches name indices from feature parameters for "Stylistic Set" ('ssXX') or
  * "Character Variant" ('cvXX') features.
  *
- * Return value: %true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 2.0.0
  **/
diff --git a/src/hb-ot-math.cc b/src/hb-ot-math.cc
index 9d8c6e735..5781d25f2 100644
--- a/src/hb-ot-math.cc
+++ b/src/hb-ot-math.cc
@@ -56,7 +56,7 @@
  *
  * Tests whether a face has a `MATH` table.
  *
- * Return value: true if the table is found, false otherwise
+ * Return value: %true if the table is found, %false otherwise
  *
  * Since: 1.3.3
  **/
@@ -142,7 +142,7 @@ hb_ot_math_get_glyph_top_accent_attachment (hb_font_t *font,
  *
  * Tests whether the given glyph index is an extended shape in the face.
  *
- * Return value: true if the glyph is an extended shape, false otherwise
+ * Return value: %true if the glyph is an extended shape, %false otherwise
  *
  * Since: 1.3.3
  **/
diff --git a/src/hb-ot-var.cc b/src/hb-ot-var.cc
index 1fe57383c..29a4c2ced 100644
--- a/src/hb-ot-var.cc
+++ b/src/hb-ot-var.cc
@@ -56,7 +56,7 @@
  *
  * Tests whether a face includes any OpenType variation data in the `fvar` table.
  *
- * Return value: true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 1.4.2
  **/
@@ -162,7 +162,7 @@ hb_ot_var_get_axis_infos (hb_face_t             *face,
  * Fetches the variation-axis information corresponding to the specified axis tag
  * in the specified face.
  *
- * Return value: true if data found, false otherwise
+ * Return value: %true if data found, %false otherwise
  *
  * Since: 2.2.0
  **/
diff --git a/src/hb-sanitize.hh b/src/hb-sanitize.hh
index 024b4d1c9..ef26ba29f 100644
--- a/src/hb-sanitize.hh
+++ b/src/hb-sanitize.hh
@@ -73,7 +73,7 @@
  * === The sanitize() contract ===
  *
  * The sanitize() method of each object type shall return true if it's safe to
- * call other methods of the object, and false otherwise.
+ * call other methods of the object, and %false otherwise.
  *
  * Note that what sanitize() checks for might align with what the specification
  * describes as valid table data, but does not have to be.  In particular, we
diff --git a/src/hb-set.cc b/src/hb-set.cc
index 3b4059ad3..e94b9fcfc 100644
--- a/src/hb-set.cc
+++ b/src/hb-set.cc
@@ -162,7 +162,7 @@ hb_set_get_user_data (hb_set_t           *set,
  *
  * Tests whether memory allocation for a set was successful.
  *
- * Return value: %true if allocation succeeded, false otherwise
+ * Return value: %true if allocation succeeded, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -209,7 +209,7 @@ hb_set_is_empty (const hb_set_t *set)
  *
  * Tests whether @codepoint belongs to @set.
  *
- * Return value: %true if @codepoint is in @set, false otherwise
+ * Return value: %true if @codepoint is in @set, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -298,7 +298,7 @@ hb_set_del_range (hb_set_t       *set,
  * Tests whether @set and @other are equal (contain the same
  * elements).
  *
- * Return value: %TRUE if the two sets are equal, %FALSE otherwise.
+ * Return value: %true if the two sets are equal, %false otherwise.
  *
  * Since: 0.9.7
  **/
@@ -316,7 +316,7 @@ hb_set_is_equal (const hb_set_t *set,
  *
  * Tests whether @set is a subset of @larger_set.
  *
- * Return value: %TRUE if the @set is a subset of (or equal to) @larger_set, %FALSE otherwise.
+ * Return value: %true if the @set is a subset of (or equal to) @larger_set, %false otherwise.
  *
  * Since: 1.8.1
  **/
@@ -483,7 +483,7 @@ hb_set_get_max (const hb_set_t *set)
  *
  * Set @codepoint to %HB_SET_VALUE_INVALID to get started.
  *
- * Return value: %true if there was a next value, false otherwise
+ * Return value: %true if there was a next value, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -504,7 +504,7 @@ hb_set_next (const hb_set_t *set,
  *
  * Set @codepoint to %HB_SET_VALUE_INVALID to get started.
  *
- * Return value: %true if there was a previous value, false otherwise
+ * Return value: %true if there was a previous value, %false otherwise
  *
  * Since: 1.8.0
  **/
@@ -527,7 +527,7 @@ hb_set_previous (const hb_set_t *set,
  *
  * Set @last to %HB_SET_VALUE_INVALID to get started.
  *
- * Return value: %true if there was a next range, false otherwise
+ * Return value: %true if there was a next range, %false otherwise
  *
  * Since: 0.9.7
  **/
@@ -551,7 +551,7 @@ hb_set_next_range (const hb_set_t *set,
  *
  * Set @first to %HB_SET_VALUE_INVALID to get started.
  *
- * Return value: %true if there was a previous range, false otherwise
+ * Return value: %true if there was a previous range, %false otherwise
  *
  * Since: 1.8.0
  **/
diff --git a/src/hb-unicode.cc b/src/hb-unicode.cc
index d7f6a6e13..8fc8f3e40 100644
--- a/src/hb-unicode.cc
+++ b/src/hb-unicode.cc
@@ -340,7 +340,7 @@ hb_unicode_funcs_make_immutable (hb_unicode_funcs_t *ufuncs)
  * Tests whether the specified Unicode-functions structure
  * is immutable.
  *
- * Return value: %true if @ufuncs is immutable, false otherwise
+ * Return value: %true if @ufuncs is immutable, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -421,7 +421,7 @@ HB_UNICODE_FUNCS_IMPLEMENT_CALLBACKS_SIMPLE
  * Calls the composition function of the specified
  * Unicode-functions structure @ufuncs.
  *
- * Return value: %true if @a and @b composed, false otherwise
+ * Return value: %true if @a and @b composed, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -446,7 +446,7 @@ hb_unicode_compose (hb_unicode_funcs_t *ufuncs,
  * Calls the decomposition function of the specified
  * Unicode-functions structure @ufuncs.
  *
- * Return value: %true if @ab was decomposed, false otherwise
+ * Return value: %true if @ab was decomposed, %false otherwise
  *
  * Since: 0.9.2
  **/
diff --git a/src/hb-unicode.h b/src/hb-unicode.h
index 7ea0848c0..3cfeab119 100644
--- a/src/hb-unicode.h
+++ b/src/hb-unicode.h
@@ -427,7 +427,7 @@ typedef hb_script_t			(*hb_unicode_script_func_t)		(hb_unicode_funcs_t *ufuncs,
  * The method must return an #hb_bool_t indicating the success
  * of the composition.
  * 
- * Return value: True is @a,@b composed, false otherwise
+ * Return value: %true is @a,@b composed, %false otherwise
  *
  **/
 typedef hb_bool_t			(*hb_unicode_compose_func_t)		(hb_unicode_funcs_t *ufuncs,
@@ -451,7 +451,7 @@ typedef hb_bool_t			(*hb_unicode_compose_func_t)		(hb_unicode_funcs_t *ufuncs,
  * output parameters (if successful). The method must return an
  * #hb_bool_t indicating the success of the composition.
  * 
- * Return value: True if @ab decomposed, false otherwise
+ * Return value: %true if @ab decomposed, %false otherwise
  *
  **/
 typedef hb_bool_t			(*hb_unicode_decompose_func_t)		(hb_unicode_funcs_t *ufuncs,
@@ -634,7 +634,7 @@ hb_unicode_script (hb_unicode_funcs_t *ufuncs,
  * Composes the code point sequence @a,@b by canonical equivalence into
  * code point @ab.
  *
- * Return value: True is @a,@b composed, false otherwise
+ * Return value: %true if @a,@b composed, %false otherwise
  *
  * Since: 0.9.2
  **/
@@ -654,7 +654,7 @@ hb_unicode_compose (hb_unicode_funcs_t *ufuncs,
  * Decomposes code point @ab by canonical equivalence, into code points
  * @a and @b.
  *
- * Return value: True if @ab decomposed, false otherwise
+ * Return value: %true if @ab decomposed, %false otherwise
  *
  * Since: 0.9.2
  **/