Usermanual: minor wording updates, build fixes.

docs/usermanual-buffers-language-script-and-direction.xml

+<?xml version="1.0"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
+  <!ENTITY % local.common.attrib "xmlns:xi  CDATA  #FIXED 'http://www.w3.org/2003/XInclude'">
+  <!ENTITY version SYSTEM "version.xml">
+]>
 <chapter id="buffers-language-script-and-direction">
   <title>Buffers, language, script and direction</title>
   <para>
@@ -74,4 +80,4 @@ void somefunc(hb_buffer_t *buffer) {
     <para>
     </para>
   </section>
-</chapter>
\ No newline at end of file
+</chapter>

docs/usermanual-clusters.xml

+<?xml version="1.0"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
+  <!ENTITY % local.common.attrib "xmlns:xi  CDATA  #FIXED 'http://www.w3.org/2003/XInclude'">
+  <!ENTITY version SYSTEM "version.xml">
+]>
 <chapter id="clusters">
 <sect1 id="clusters">
   <title>Clusters</title>

docs/usermanual-fonts-and-faces.xml

+<?xml version="1.0"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
+  <!ENTITY % local.common.attrib "xmlns:xi  CDATA  #FIXED 'http://www.w3.org/2003/XInclude'">
+  <!ENTITY version SYSTEM "version.xml">
+]>
 <chapter id="fonts-and-faces">
   <title>Fonts and faces</title>
   <section id="using-freetype">
@@ -15,4 +21,4 @@
     <para>
     </para>
   </section>
-</chapter>
\ No newline at end of file
+</chapter>

docs/usermanual-getting-started.xml

+<?xml version="1.0"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
+  <!ENTITY % local.common.attrib "xmlns:xi  CDATA  #FIXED 'http://www.w3.org/2003/XInclude'">
+  <!ENTITY version SYSTEM "version.xml">
+]>
 <chapter id="getting-started">
   <title>Getting started with HarfBuzz</title>
   <section>

docs/usermanual-glyph-information.xml

+<?xml version="1.0"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
+  <!ENTITY % local.common.attrib "xmlns:xi  CDATA  #FIXED 'http://www.w3.org/2003/XInclude'">
+  <!ENTITY version SYSTEM "version.xml">
+]>
 <sect1 id="glyph-information">
   <title>Glyph information</title>
   <sect2 id="names-and-numbers">
@@ -5,4 +11,4 @@
     <para>
     </para>
   </sect2>
-</sect1>
\ No newline at end of file
+</sect1>

docs/usermanual-install-harfbuzz.xml

+<?xml version="1.0"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
+  <!ENTITY % local.common.attrib "xmlns:xi  CDATA  #FIXED 'http://www.w3.org/2003/XInclude'">
+  <!ENTITY version SYSTEM "version.xml">
+]>
 <chapter id="install-harfbuzz">
   <title>Installing HarfBuzz</title>
   
@@ -376,11 +382,16 @@
 	  <term>--with-uniscribe</term>
 	  <listitem>
 	    <para>
-	      Use the <ulink url="https://docs.microsoft.com/en-us/windows/desktop/intl/uniscribe">Uniscribe</ulink> library. <emphasis>(Default = no)</emphasis>
+	      Use the <ulink
+	      url="https://docs.microsoft.com/en-us/windows/desktop/intl/uniscribe">Uniscribe</ulink>
+	      library (experimental). <emphasis>(Default = no)</emphasis>
 	    </para>	    
 	    <para>
 	      This option enables or disables usage of the Uniscribe
-	      font-rendering library. Uniscribe is available on Windows systems.
+	      font-rendering library. Uniscribe is available on
+	      Windows systems. Uniscribe support is used only for
+	      testing purposes and does not need to be enabled for
+	      HarfBuzz to run on Windows systems.
 	    </para>
 	  </listitem>
 	</varlistentry>
@@ -393,7 +404,10 @@
 	    </para>	    
 	    <para>
 	      This option enables or disables usage of the DirectWrite
-	      font-rendering library. DirectWrite is available on Windows systems.
+	      font-rendering library. DirectWrite is available on
+	      Windows systems. DirectWrite support is used only for
+	      testing purposes and does not need to be enabled for
+	      HarfBuzz to run on Windows systems.
 	    </para>
 	  </listitem>
 	</varlistentry>

docs/usermanual-opentype-features.xml

+<?xml version="1.0"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
+  <!ENTITY % local.common.attrib "xmlns:xi  CDATA  #FIXED 'http://www.w3.org/2003/XInclude'">
+  <!ENTITY version SYSTEM "version.xml">
+]>
 <chapter id="shaping-and-shape-plans">
   <title>Shaping and shape plans</title>
   <section id="opentype-features">
@@ -10,4 +16,4 @@
     <para>
     </para>
   </section>
-</chapter>
\ No newline at end of file
+</chapter>

docs/usermanual-shaping-concepts.xml

+<?xml version="1.0"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
+  <!ENTITY % local.common.attrib "xmlns:xi  CDATA  #FIXED 'http://www.w3.org/2003/XInclude'">
+  <!ENTITY version SYSTEM "version.xml">
+]>
 <chapter id="shaping-concepts">
   <title>Shaping concepts</title>
   <section id="text-shaping-concepts">

docs/usermanual-what-is-harfbuzz.xml

@@ -91,7 +91,8 @@
       engines in Firefox, LibreOffice, and Chromium. Unless you are
       <emphasis>writing</emphasis> one of these layout engines
       yourself, you will probably not need to use HarfBuzz: normally,
-      lower-level libraries will turn text into glyphs for you.
+      a layout engine, toolkit, or other library will turn text into
+      glyphs for you.
     </para>
     <para>
       However, if you <emphasis>are</emphasis> writing a layout engine
@@ -301,8 +302,8 @@
 
     <para>
       In addition to OpenType shaping, HarfBuzz supports the latest
-      version of Graphite shaping. HarfBuzz currently supports AAT
-      shaping only on macOS and iOS systems.
+      version of Graphite shaping (the "Graphite 2" model) and AAT
+      shaping.
     </para>
     
     <para>
@@ -313,8 +314,9 @@
     </para>
 
     <para>
-      HarfBuzz can run on top of the FreeType, CoreText, DirectWrite,
-      or Uniscribe font renderers.
+      HarfBuzz is designed and tested to run on top of the FreeType
+      font renderer. It can run on Linux, Android, Windows, macOS, and
+      iOS systems.
     </para>
     
     <para>