+Note: From time to time, changes are made in Gnulib that are not backward
+compatible. When updating to a more recent Gnulib, you should consult
+Gnulib's @file{NEWS} file to check whether the incompatible changes affect
+your project.
+
+
+@node Source changes
+@section Changing your sources for use with Gnulib
+
+Gnulib contains some header file overrides. This means that when building
+on systems with deficient header files in @file{/usr/include/}, it may create
+files named @file{string.h}, @file{stdlib.h}, @file{stdint.h} or similar in
+the build directory. In the other source directories of your package you
+will usually pass @samp{-I} options to the compiler, so that these Gnulib
+substitutes are visible and take precedence over the files in
+@file{/usr/include/}.
+
+These Gnulib substitute header files rely on @file{<config.h>} being
+already included. Furthermore @file{<config.h>} must be the first include
+in every compilation unit. This means that to @emph{all your source files}
+and likely also to @emph{all your tests source files} you need to add an
+@samp{#include <config.h>} at the top. Which source files are affected?
+Exactly those whose compilation includes a @samp{-I} option that refers to
+the Gnulib library directory.
+
+This is annoying, but inevitable: On many systems, @file{<config.h>} is
+used to set system dependent flags (such as @code{_GNU_SOURCE} on GNU systems),
+and these flags have no effect after any system header file has been included.
+
+
+@node gettextize and autopoint
+@section Caveat: @code{gettextize} and @code{autopoint} users
+
+@cindex gettextize, caveat
+@cindex autopoint, caveat
+The programs @code{gettextize} and @code{autopoint}, part of
+GNU @code{gettext}, import or update the internationalization infrastructure.
+Some of this infrastructure, namely ca.@: 20 autoconf macro files and the
+@file{config.rpath} file, is also contained in Gnulib and may be imported
+by @code{gnulib-tool}. The use of @code{gettextize} or @code{autopoint}
+will therefore overwrite some of the files that @code{gnulib-tool} has
+imported, and vice versa.
+
+Avoiding to use @code{gettextize} (manually, as package maintainer) or
+@code{autopoint} (as part of a script like @code{autoreconf} or
+@code{autogen.sh}) is not the solution: These programs also import the
+infrastructure in the @file{po/} and optionally in the @file{intl/} directory.
+
+The copies of the conflicting files in Gnulib are more up-to-date than
+the copies brought in by @code{gettextize} and @code{autopoint}. When a
+new @code{gettext} release is made, the copies of the files in Gnulib will
+be updated immediately.
+
+The solution is therefore:
+
+@enumerate
+@item
+When you run @code{gettextize}, always use the @code{gettextize} from the
+matching GNU gettext release. For the most recent Gnulib checkout, this is
+the newest release found on @url{http://ftp.gnu.org/gnu/gettext/}. For an
+older Gnulib snapshot, it is the release that was the most recent release
+at the time the Gnulib snapshot was taken. Then, after @code{gettextize},
+invoke @code{gnulib-tool}.
+
+@item
+When a script of yours run @code{autopoint}, invoke @code{gnulib-tool}
+afterwards.
+
+@item
+If you get an error message like
+@code{*** error: gettext infrastructure mismatch:
+using a Makefile.in.in from gettext version ...
+but the autoconf macros are from gettext version ...},
+it means that a new GNU gettext release was made, and its autoconf macros
+were integrated into Gnulib and now mismatch the @file{po/} infrastructure.
+In this case, fetch and install the new GNU gettext release and run
+@code{gettextize} followed by @code{gnulib-tool}.
+
+@item
+When you invoke @code{autoreconf} after @code{gnulib-tool}, make sure to
+not invoke @code{autopoint} a second time, by setting the @code{AUTOPOINT}
+environment variable, like this:
+@smallexample
+$ env AUTOPOINT=true autoreconf --install
+@end smallexample
+@end enumerate
+
+
+@node Localization
+@section Handling Gnulib's own message translations
+
+Gnulib provides some functions that emit translatable messages using GNU
+@code{gettext}. The @samp{gnulib} domain at the
+@url{http://translationproject.org/, Translation Project} collects
+translations of these messages, which you should incorporate into your
+own programs.
+
+There are two basic ways to achieve this. The first, and older, method
+is to list all the source files you use from Gnulib in your own
+@file{po/POTFILES.in} file. This will cause all the relevant
+translatable strings to be included in your POT file. When you send
+this POT file to the Translation Project, translators will normally fill
+in the translations of the Gnulib strings from their ``translation
+memory'', and send you back updated PO files.
+
+However, this process is error-prone: you might forget to list some
+source files, or the translator might not be using a translation memory
+and provide a different translation than another translator, or the
+translation might not be kept in sync between Gnulib and your package.
+It is also slow and causes substantial extra work, because a human
+translator must be in the loop for each language and you will need to
+incorporate their work on request.
+
+For these reasons, a new method was designed and is now recommended. If
+you pass the @code{--po-base=@var{directory}} and @code{--po-domain=@var{domain}}
+options to @code{gnulib-tool}, then @code{gnulib-tool} will create a
+separate directory with its own @file{POTFILES.in}, and fetch current
+translations directly from the Translation Project (using
+@command{rsync} or @command{wget}, whichever is available).
+The POT file in this directory will be called
+@file{@var{domain}-gnulib.pot}, depending on the @var{domain} you gave to the
+@code{--po-domain} option (typically the same as the package name).
+This causes these translations to reside in a separate message domain,
+so that they do not clash either with the translations for the main part
+of your package nor with those of other packages on the system that use
+possibly different versions of Gnulib.
+When you use these options, the functions in Gnulib are built
+in such a way that they will always use this domain regardless of the
+default domain set by @code{textdomain}.
+
+In order to use this method, you must -- in each program that might use
+Gnulib code -- add an extra line to the part of the program that
+initializes locale-dependent behavior. Where you would normally write
+something like:
+
+@example
+@group
+ setlocale (LC_ALL, "");
+ bindtextdomain (PACKAGE, LOCALEDIR);
+ textdomain (PACKAGE);
+@end group
+@end example
+
+@noindent
+you should add an additional @code{bindtextdomain} call to inform
+gettext of where the MO files for the extra message domain may be found:
+
+@example
+@group
+ bindtextdomain (PACKAGE "-gnulib", LOCALEDIR);
+@end group
+@end example
+
+(This example assumes that the @var{domain} that you specified
+to @code{gnulib-tool} is the same as the value of the @code{PACKAGE}
+preprocessor macro.)
+
+Since you do not change the @code{textdomain} call, the default message
+domain for your program remains the same and your own use of @code{gettext}
+functions will not be affected.
+
+
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