Update the various INSTALL files

* nt/INSTALL.W64:
* nt/INSTALL:
* INSTALL: Update the installation information, in particular the
fact that HarfBuzz is now preferred as the shaping library.

1 files changed, 20 insertions, 14 deletions

diff --git a/INSTALL b/INSTALL
index 4d65f302aac..cb1fe8d3c2c 100644
--- a/INSTALL
+++ b/INSTALL
@@ -117,19 +117,25 @@ ADDITIONAL DISTRIBUTION FILES
 
 * Complex Text Layout support libraries
 
-On GNU and Unix systems, Emacs needs the optional libraries "m17n-db",
-"libm17n-flt", "libotf" to correctly display such complex scripts as
-Indic and Khmer, and also for scripts that require Arabic shaping
-support (Arabic and Farsi).  On some systems, particularly GNU/Linux,
-these libraries may be already present or available as additional
-packages.  Note that if there is a separate 'dev' or 'devel' package,
-for use at compilation time rather than run time, you will need that
-as well as the corresponding run time package; typically the dev
-package will contain header files and a library archive.  Otherwise,
-you can download the libraries from <https://www.nongnu.org/m17n/>.
+On GNU and Unix systems, Emacs needs optional libraries to correctly
+display such complex scripts as Indic and Khmer, and also for scripts
+that require Arabic shaping support (Arabic and Farsi).  If the
+HarfBuzz library is installed, Emacs will build with it and use it for
+this purpose.  HarfBuzz is the preferred shaping engine, both on Posix
+hosts and on MS-Windows, so we recommend installing it before building
+Emacs.  The alternative for GNU/Linux and Posix systems is to use the
+"m17n-db", "libm17n-flt", and "libotf" libraries.  (On some systems,
+particularly GNU/Linux, these libraries may be already present or
+available as additional packages.)  Note that if there is a separate
+'dev' or 'devel' package, for use at compilation time rather than run
+time, you will need that as well as the corresponding run time
+package; typically the dev package will contain header files and a
+library archive.  On MS-Windows, if HarfBuzz is not available, Emacs
+will use the Uniscribe shaping engine that is part of the OS.
 
 Note that Emacs cannot support complex scripts on a TTY, unless the
-terminal includes such a support.
+terminal includes such a support.  However, most modern terminal
+emulators, such as xterm, do support such scripts.
 
 * intlfonts-VERSION.tar.gz
 
@@ -234,10 +240,10 @@ directory.  On Red Hat-based systems, the corresponding command is
 config-manager --set-enabled fedora-debuginfo updates-debuginfo').
 
 Once you have installed the source package, for example at
-/path/to/emacs-26.1, add the following line to your startup file:
+/path/to/emacs-27.1, add the following line to your startup file:
 
      (setq find-function-C-source-directory
-           "/path/to/emacs-26.1/src")
+           "/path/to/emacs-27.1/src")
 
 The installation directory of the Emacs source package will contain
 the exact package name and version number Emacs is installed on your
@@ -249,7 +255,7 @@ Emacs debugging symbols are distributed by a debug package.  It does
 not exist for every released Emacs package, this depends on the
 distribution.  On Debian-based systems, you can install a debug
 package of Emacs with a command like 'apt-get install emacs-dbg' (on
-older systems, replace 'emacs' with eg 'emacs25').  On Red Hat-based
+older systems, replace 'emacs' with eg 'emacs27').  On Red Hat-based
 systems, the corresponding command is 'dnf debuginfo-install emacs'.