[style] Fix documentation

Message documentation a bit to get it working.

docs/harfbuzz-docs.xml

@@ -97,6 +97,11 @@
         <xi:include href="xml/hb-directwrite.xml"/>
       </chapter>
 
+      <chapter id="style-api">
+        <title>Style API</title>
+        <xi:include href="xml/hb-style.xml"/>
+      </chapter>
+
       <chapter id="subset-api">
         <title>Subset API</title>
         <xi:include href="xml/hb-subset.xml"/>

docs/harfbuzz-sections.txt

@@ -707,6 +707,12 @@ hb_version_atleast
 hb_version_string
 </SECTION>
 
+<SECTION>
+<FILE>hb-style</FILE>
+hb_style_tag_t
+hb_style_get_value
+</SECTION>
+
 <SECTION>
 <FILE>hb-subset</FILE>
 hb_subset_flags_t

src/hb-style.cc

@@ -34,6 +34,15 @@
 #include "hb-ot-post-table.hh"
 #include "hb-ot-face.hh"
 
+/**
+ * SECTION:hb-style
+ * @title: hb-style
+ * @short_description: Font Styles
+ * @include: hb.h
+ *
+ * Functions for fetching style information from fonts.
+ **/
+
 static inline float
 _hb_angle_to_ratio (float a)
 {
@@ -52,7 +61,7 @@ _hb_ratio_to_angle (float r)
  * @font: a #hb_font_t object.
  * @style_tag: a style tag.
  *
- * Searches variation axes of a hb_font_t object for a specific axis first,
+ * Searches variation axes of a #hb_font_t object for a specific axis first,
  * if not set, then tries to get default style values from different
  * tables of the font.
  *

src/hb-style.h

@@ -44,6 +44,7 @@ HB_BEGIN_DECLS
  * must be greater than -90 and less than +90. Values can be interpreted as
  * the angle, in counter-clockwise degrees, of oblique slant from whatever the
  * designer considers to be upright for that font design.
+ * @HB_STYLE_TAG_SLANT_RATIO: same as @HB_STYLE_TAG_SLANT_ANGLE expression as ratio.
  * @HB_STYLE_TAG_WIDTH: Used to vary width of text from narrower to wider.
  * Non-zero. Values can be interpreted as a percentage of whatever the font
  * designer considers “normal width” for that font design.
@@ -52,7 +53,7 @@ HB_BEGIN_DECLS
  * comparison to values for usWeightClass in the OS/2 table,
  * or the CSS font-weight property.
  *
- * Defined by https://docs.microsoft.com/en-us/typography/opentype/spec/dvaraxisreg
+ * Defined by [OpenType Design-Variation Axis Tag Registry](https://docs.microsoft.com/en-us/typography/opentype/spec/dvaraxisreg).
  *
  * Since: REPLACEME
  **/