diff --git a/docs/harfbuzz-sections.txt b/docs/harfbuzz-sections.txt
index 85b0fa7d9..621029c77 100644
--- a/docs/harfbuzz-sections.txt
+++ b/docs/harfbuzz-sections.txt
@@ -600,6 +600,8 @@ hb_ot_layout_language_get_required_feature_index
 Xhb_ot_layout_lookup_enumerate_sequences
 Xhb_ot_layout_lookup_position
 Xhb_ot_layout_lookup_substitute
+hb_ot_layout_glyph_sequence_t
+hb_ot_layout_glyph_sequence_func_t
 </SECTION>
 
 <SECTION>
diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 91a56c552..17cff3fb0 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -410,7 +410,7 @@ get_gsubgpos_table (hb_face_t *face,
 /**
  * hb_ot_layout_table_get_script_tags:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @start_offset: offset of the first script tag to retrieve
  * @script_count: (inout) (allow-none): Input = the maximum number of script tags to return;
  *                Output = the actual number of script tags returned (may be zero)
@@ -437,7 +437,7 @@ hb_ot_layout_table_get_script_tags (hb_face_t    *face,
 /**
  * hb_ot_layout_table_find_script:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @script_tag: #hb_tag_t of the script tag requested
  * @script_index: (out): The index of the requested script tag
  *
@@ -481,7 +481,7 @@ hb_ot_layout_table_find_script (hb_face_t    *face,
 /**
  * hb_ot_layout_table_choose_script:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @script_tags: Array of #hb_tag_t script tags
  * @script_index: (out): The index of the requested script tag
  * @chosen_script: (out): #hb_tag_t of the script tag requested
@@ -504,11 +504,22 @@ hb_ot_layout_table_choose_script (hb_face_t      *face,
 /**
  * hb_ot_layout_table_select_script:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @script_count: Number of script tags in the array
  * @script_tags: Array of #hb_tag_t script tags
- * @script_index: (out): The index of the requested script
- * @chosen_script: (out): #hb_tag_t of the requested script
+ * @script_index: (out) (optional): The index of the requested script
+ * @chosen_script: (out) (optional): #hb_tag_t of the requested script
+ *
+ * Selects an OpenType script for @table_tag from the @script_tags array.
+ *
+ * If the table does not have any of the requested scripts, then `DFLT`,
+ * `dflt`, and `latn` tags are tried in that order. If the table still does not
+ * have any of these scripts, @script_index and @chosen_script are set to
+ * #HB_OT_LAYOUT_NO_SCRIPT_INDEX.
+ *
+ * Return value:
+ * %true if one of the requested scripts is selected, %false if a fallback
+ * script is selected or if no scripts are selected.
  *
  * Since: 2.0.0
  **/
@@ -566,7 +577,7 @@ hb_ot_layout_table_select_script (hb_face_t      *face,
 /**
  * hb_ot_layout_table_get_feature_tags:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @start_offset: offset of the first feature tag to retrieve
  * @feature_count: (inout) (allow-none): Input = the maximum number of feature tags to return;
  *                 Output = the actual number of feature tags returned (may be zero)
@@ -591,7 +602,7 @@ hb_ot_layout_table_get_feature_tags (hb_face_t    *face,
 /**
  * hb_ot_layout_table_find_feature:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @feature_tag: The #hb_tag_t og the requested feature tag
  * @feature_index: (out): The index of the requested feature
  *
@@ -626,7 +637,7 @@ hb_ot_layout_table_find_feature (hb_face_t    *face,
 /**
  * hb_ot_layout_script_get_language_tags:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @script_index: The index of the requested script tag
  * @start_offset: offset of the first language tag to retrieve
  * @language_count: (inout) (allow-none): Input = the maximum number of language tags to return;
@@ -655,7 +666,7 @@ hb_ot_layout_script_get_language_tags (hb_face_t    *face,
 /**
  * hb_ot_layout_script_find_language:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @script_index: The index of the requested script tag
  * @language_tag: The #hb_tag_t of the requested language
  * @language_index: The index of the requested language
@@ -688,7 +699,7 @@ hb_ot_layout_script_find_language (hb_face_t    *face,
 /**
  * hb_ot_layout_script_select_language:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @script_index: The index of the requested script tag
  * @language_count: The number of languages in the specified script
  * @language_tags: The array of language tags
@@ -731,7 +742,7 @@ hb_ot_layout_script_select_language (hb_face_t      *face,
 /**
  * hb_ot_layout_language_get_required_feature_index:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @script_index: The index of the requested script tag
  * @language_index: The index of the requested language tag
  * @feature_index: (out): The index of the requested feature
@@ -761,7 +772,7 @@ hb_ot_layout_language_get_required_feature_index (hb_face_t    *face,
 /**
  * hb_ot_layout_language_get_required_feature:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @script_index: The index of the requested script tag
  * @language_index: The index of the requested language tag
  * @feature_index: (out): The index of the requested feature
@@ -796,7 +807,7 @@ hb_ot_layout_language_get_required_feature (hb_face_t    *face,
 /**
  * hb_ot_layout_language_get_feature_indexes:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @script_index: The index of the requested script tag
  * @language_index: The index of the requested language tag
  * @start_offset: offset of the first feature tag to retrieve
@@ -827,7 +838,7 @@ hb_ot_layout_language_get_feature_indexes (hb_face_t    *face,
 /**
  * hb_ot_layout_language_get_feature_tags:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @script_index: The index of the requested script tag
  * @language_index: The index of the requested language tag
  * @start_offset: offset of the first feature tag to retrieve
@@ -868,7 +879,7 @@ hb_ot_layout_language_get_feature_tags (hb_face_t    *face,
 /**
  * hb_ot_layout_language_find_feature:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @script_index: The index of the requested script tag
  * @language_index: The index of the requested language tag
  * @feature_tag: #hb_tag_t of the feature tag requested
@@ -910,7 +921,7 @@ hb_ot_layout_language_find_feature (hb_face_t    *face,
 /**
  * hb_ot_layout_feature_get_lookups:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @feature_index: The index of the requested feature
  * @start_offset: offset of the first lookup to retrieve
  * @lookup_count: (inout) (allow-none): Input = the maximum number of lookups to return;
@@ -944,7 +955,7 @@ hb_ot_layout_feature_get_lookups (hb_face_t    *face,
 /**
  * hb_ot_layout_table_get_lookup_count:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  *
  * Fetches the total number of lookups enumerated in the specified
  * face's GSUB table or GPOS table.
@@ -1101,7 +1112,7 @@ script_collect_features (hb_collect_features_context_t *c,
 /**
  * hb_ot_layout_collect_features:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @scripts: The array of scripts to collect features for
  * @languages: The array of languages to collect features for
  * @features: The array of features to collect
@@ -1152,7 +1163,7 @@ hb_ot_layout_collect_features (hb_face_t      *face,
 /**
  * hb_ot_layout_collect_lookups:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @scripts: The array of scripts to collect lookups for
  * @languages: The array of languages to collect lookups for
  * @features: The array of features to collect lookups for
@@ -1191,7 +1202,7 @@ hb_ot_layout_collect_lookups (hb_face_t      *face,
 /**
  * hb_ot_layout_lookup_collect_glyphs:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @lookup_index: The index of the feature lookup to query
  * @glyphs_before: (out): Array of glyphs preceding the substitution range
  * @glyphs_input: (out): Array of input glyphs that would be substituted by the lookup
@@ -1243,7 +1254,7 @@ hb_ot_layout_lookup_collect_glyphs (hb_face_t    *face,
 /**
  * hb_ot_layout_table_find_feature_variations:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @coords: The variation coordinates to query
  * @num_coords: The number of variation coordinates
  * @variations_index: (out): The array of feature variations found for the query
@@ -1268,7 +1279,7 @@ hb_ot_layout_table_find_feature_variations (hb_face_t    *face,
 /**
  * hb_ot_layout_feature_with_variations_get_lookups:
  * @face: #hb_face_t to work upon
- * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
+ * @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
  * @feature_index: The index of the feature to query
  * @variations_index: The index of the feature variation to query
  * @start_offset: offset of the first lookup to retrieve
@@ -1488,6 +1499,8 @@ hb_ot_layout_lookups_substitute_closure (hb_face_t      *face,
  * hb_ot_layout_has_positioning:
  * @face: #hb_face_t to work upon
  *
+ * Tests whether the specified face includes any GPOS positioning.
+ *
  * Return value: %true if the face has GPOS data, %false otherwise
  *
  **/
diff --git a/src/hb-ot-layout.h b/src/hb-ot-layout.h
index 54dd780df..57529921d 100644
--- a/src/hb-ot-layout.h
+++ b/src/hb-ot-layout.h
@@ -38,10 +38,35 @@
 HB_BEGIN_DECLS
 
 
+/**
+ * HB_OT_TAG_BASE:
+ *
+ * OpenType [Baseline Table](https://docs.microsoft.com/en-us/typography/opentype/spec/base).
+ */
 #define HB_OT_TAG_BASE HB_TAG('B','A','S','E')
+/**
+ * HB_OT_TAG_GDEF:
+ *
+ * OpenType [Glyph Definition Table](https://docs.microsoft.com/en-us/typography/opentype/spec/gdef).
+ */
 #define HB_OT_TAG_GDEF HB_TAG('G','D','E','F')
+/**
+ * HB_OT_TAG_GSUB:
+ *
+ * OpenType [Glyph Substitution Table](https://docs.microsoft.com/en-us/typography/opentype/spec/gsub).
+ */
 #define HB_OT_TAG_GSUB HB_TAG('G','S','U','B')
+/**
+ * HB_OT_TAG_GPOS:
+ *
+ * OpenType [Glyph Positioning Table](https://docs.microsoft.com/en-us/typography/opentype/spec/gpos).
+ */
 #define HB_OT_TAG_GPOS HB_TAG('G','P','O','S')
+/**
+ * HB_OT_TAG_JSTF:
+ *
+ * OpenType [Justification Table](https://docs.microsoft.com/en-us/typography/opentype/spec/jstf).
+ */
 #define HB_OT_TAG_JSTF HB_TAG('J','S','T','F')
 
 
@@ -55,12 +80,16 @@ HB_BEGIN_DECLS
 /**
  * HB_OT_MAX_TAGS_PER_SCRIPT:
  *
+ * Maximum number of OpenType tags that can correspond to a give #hb_script_t.
+ *
  * Since: 2.0.0
  **/
 #define HB_OT_MAX_TAGS_PER_SCRIPT	3u
 /**
  * HB_OT_MAX_TAGS_PER_LANGUAGE:
  *
+ * Maximum number of OpenType tags that can correspond to a give #hb_language_t.
+ *
  * Since: 2.0.0
  **/
 #define HB_OT_MAX_TAGS_PER_LANGUAGE	3u
@@ -144,9 +173,29 @@ hb_ot_layout_get_ligature_carets (hb_font_t      *font,
  * GSUB/GPOS feature query and enumeration interface
  */
 
+/**
+ * HB_OT_LAYOUT_NO_SCRIPT_INDEX:
+ *
+ * Special value for script index indicating unsupported script.
+ */
 #define HB_OT_LAYOUT_NO_SCRIPT_INDEX		0xFFFFu
+/**
+ * HB_OT_LAYOUT_NO_FEATURE_INDEX:
+ *
+ * Special value for feature index indicating unsupported feature.
+ */
 #define HB_OT_LAYOUT_NO_FEATURE_INDEX		0xFFFFu
+/**
+ * HB_OT_LAYOUT_DEFAULT_LANGUAGE_INDEX:
+ *
+ * Special value for language index indicating default or unsupported language.
+ */
 #define HB_OT_LAYOUT_DEFAULT_LANGUAGE_INDEX	0xFFFFu
+/**
+ * HB_OT_LAYOUT_NO_VARIATIONS_INDEX:
+ *
+ * Special value for variations index indicating unsupported variation.
+ */
 #define HB_OT_LAYOUT_NO_VARIATIONS_INDEX	0xFFFFFFFFu
 
 HB_EXTERN unsigned int
@@ -433,7 +482,7 @@ hb_ot_layout_feature_get_characters (hb_face_t      *face,
  * @HB_OT_LAYOUT_BASELINE_TAG_MATH: The baseline about which mathematical characters are centered.
  * In vertical writing mode when mathematical characters rotated 90 degrees clockwise, are centered.
  *
- * Baseline tags from https://docs.microsoft.com/en-us/typography/opentype/spec/baselinetags
+ * Baseline tags from [Baseline Tags](https://docs.microsoft.com/en-us/typography/opentype/spec/baselinetags) registry.
  *
  * Since: 2.6.0
  */
diff --git a/src/hb-ot-tag.cc b/src/hb-ot-tag.cc
index 19bd3639d..9ced76a12 100644
--- a/src/hb-ot-tag.cc
+++ b/src/hb-ot-tag.cc
@@ -164,6 +164,15 @@ hb_ot_all_tags_from_script (hb_script_t   script,
   *count = i;
 }
 
+/**
+ * hb_ot_tag_to_script:
+ * @tag: a script tag
+ *
+ * Converts a script tag to an #hb_script_t.
+ *
+ * Return value: The #hb_script_t corresponding to @tag.
+ *
+ **/
 hb_script_t
 hb_ot_tag_to_script (hb_tag_t tag)
 {
@@ -424,10 +433,12 @@ hb_ot_tags_from_script_and_language (hb_script_t   script,
 
 /**
  * hb_ot_tag_to_language:
+ * @tag: an language tag
  *
+ * Converts a language tag to an #hb_language_t.
  *
- *
- * Return value: (transfer none):
+ * Return value: (transfer none) (nullable):
+ * The #hb_language_t corresponding to @tag.
  *
  * Since: 0.9.2
  **/