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authorKarl Berry <karl@freefriends.org>2021-02-25 19:22:25 +0000
committerKarl Berry <karl@freefriends.org>2021-02-25 19:22:25 +0000
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tree16296910eb3eca724371474ea9aea3994dc69614 /Build/source/README.4layout
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+(This file was generated by makeinfo and splitinfo.gawk.)
+(Released under the old-style GNU documentation license;
+ see sources or other output files for full text.)
+
+6 Layout and infrastructure
+***************************
+
+The TeX Live source tree is the subtree rooted at 'Build/source' of the
+complete TL distribution and contains the sources for all executables
+distributed by TL, as well as 'configure' scripts and 'make' rules to
+build and install them together with some of their support files.
+
+6.1 Build system tools
+======================
+
+As mentioned above (*note Prerequisites::), a normal build has few
+requirements. On the other hand, if you want to modify the TeX Live
+infrastructure sources, such as 'configure.ac' or 'Makefile.am' files,
+you will need to have several additional tools installed.
+
+ In general, the TL build system uses the latest released versions of
+the GNU build tools, installed directly from the original GNU releases
+(e.g., by building them with 'configure --prefix=/usr/local/gnu' and
+having 'PATH' start with '/usr/local/gnu/bin'). We have found that
+trying to use the versions of these tools packaged for distros causes
+many extra hassles, so don't do that, tempting as it may be.
+
+ Currently the versions we use are:
+
+ autoconf (GNU Autoconf) 2.69
+ automake (GNU automake) 1.16.1
+ bison (GNU Bison) 3.5.2
+ flex 2.6.0
+ ltmain.sh (GNU libtool) 2.4.6
+ m4 (GNU M4) 1.4.18
+ makeinfo (GNU texinfo) 6.7
+
+ These versions should be used to update the generated files (e.g.,
+'configure' or 'Makefile.in') in all or parts of the TL tree after their
+dependencies have been changed. This can be done explicitly with the
+top-level 'reautoconf' script or implicitly by using the configure
+option '--enable-maintainer-mode'.
+
+ It has often turned out that the bison and flex versions are not
+critical; however, the autotools versions are. If you don't have the
+given versions, get them before modifying the build infrastructure.
+
+ The files in the Subversion repository (see
+<https://tug.org/texlive/svn>) are all up to date (barring bugs). For
+this to be reflected by their timestamps in your checkout, be sure to
+set 'use-commit-times=yes' in '~/.subversion/config' or the equivalent.
+
+ If timestamps are wrong, you may also be able to avoid unnecessary
+runs of 'bison', 'flex', or 'makeinfo' with 'touch' of the generated
+('.c', '.h', or '.info') files. With '--enable-maintainer-mode' it may
+also be necessary to 'touch' first 'aclocal.m4', then 'configure' and
+'config.h.in' (or 'c-auto.in'), and finally all 'Makefile.in' files.
+
+6.2 Top-level directories
+=========================
+
+Here is a brief description of the top-level directories in the TeX Live
+source tree.
+
+ As mentioned at the beginning of *note Overview of build system::,
+the main source directories are 'texk/' (TeX-specific programs and
+libraries), 'utils/' (additional programs), and 'libs/' (generic
+libraries).
+
+ In addition, the top-level directories 'am/' and 'm4/' contain
+'Makefile.am' fragments and Autoconf macros, respectively, used in many
+places. Specifically, the file 'm4/kpse-pkgs.m4' contains lists of all
+program and library modules; missing modules are silently ignored.
+(This helps in creating cut-down source trees.)
+
+ Each module contributes fragments (in separate files) defining its
+capabilities and requirements to the 'configure.ac' scripts at the
+top-level and in the subdirectories 'libs', 'utils', and 'texk'. The
+fragments from program modules supply 'configure' options to disable or
+enable building them; those from library modules specify if an installed
+(system) version of that library can be used. This ultimately
+determines which modules need to be built--although all modules must be
+configured for the benefit of 'make' targets such as 'dist' or
+'distcheck'.
+
+ The top-level 'build-aux/' directory contains the common files
+'compile', 'config.guess', 'config.sub', 'depcomp', etc. used by most
+packages. These are taken from the GNU Gnulib sources
+(<https://www.gnu.org/software/gnulib>), which in turn synchronizes with
+any ultimate upstream repository. There are independent copies of some
+of these in a few other places, e.g.,
+'libs/freetype2/freetype-*/builds/unix/'. The 'reautoconf' script does
+not touch those, but a TL cron job keeps them in sync (nightly).
+
+ When the top-level './Build' script is used to build TL, two more two
+more top-level directories appear: 'Work/' for the build tree, and
+'inst/' for the install tree (from 'make install'). These names (and
+everything else about 'Build''s operation) can be changed by setting
+environment variables before running it; see the script source.
+
+6.3 Autoconf macros
+===================
+
+Here we describe a few of the Autoconf macros used in several
+modules--many more are defined in the sources; see the top-level 'm4/'
+directory. These general macros are supplemented by module-specific
+macros in directories such as 'texk/dvipng/m4/'; some of those are
+described in following sections (*note Library modules:: and *note
+Program modules::).
+
+6.3.1 General setup macros
+--------------------------
+
+The TL sources use two general setup macros:
+
+ -- Macro: KPSE_BASIC (NAME, [MORE-OPTIONS])
+ Initialize the basic TL infrastructure for module NAME:
+ 'AM_INIT_AUTOMAKE([foreign MORE-OPTIONS])'
+ 'AM_MAINTAINER_MODE'
+ 'KPSE_COMPILER_WARNINGS'
+ and make sure the C compiler understands function prototypes. This
+ is used for all generic library and program modules.
+
+ -- Macro: KPSE_COMMON (NAME, [MORE-OPTIONS])
+ Like 'KPSE_BASIC' but add:
+ 'LT_PREREQ([2.2.6])'
+ 'LT_INIT([win32-dll])'
+ 'AC_SYS_LARGEFILE'
+ 'AC_FUNC_FSEEKO'
+ along with checks for frequently used functions, headers, types,
+ and structures. This is used for TeX-specific modules.
+
+6.3.2 Macros for programs
+-------------------------
+
+Macros for program checks:
+
+ -- Macro: KPSE_CHECK_LATEX
+ Set 'LATEX' to the first of 'latex', 'elatex', or 'lambda' which
+ exists in 'PATH', or to 'no' if none of them exists. Call
+ 'AC_SUBST' for 'LATEX'. The result of this test can be overridden
+ by setting the 'LATEX' environment variable or the cache variable
+ 'ac_cv_prog_LATEX'.
+
+ -- Macro: KPSE_CHECK_PDFLATEX
+ Check for 'pdflatex' in 'PATH' and set 'PDFLATEX'.
+
+ -- Macro: KPSE_CHECK_PERL
+ Check for 'perl' or 'perl5' in 'PATH' and set 'PERL'.
+
+ -- Macro: KPSE_PROG_LEX
+ Call 'AC_PROG_LEX' and add the flag '-l' for 'flex'.
+
+6.3.3 Macros for compilers
+--------------------------
+
+Macros for compiler-related checks:
+
+ -- Macro: KPSE_COMPILER_WARNINGS
+ When using the (Objective) C/C++ compiler, set
+ 'WARNING_[OBJ]C[XX]FLAGS' to suitable warning flags (depending on
+ the value given to or implied for '--enable-compiler-warnings').
+ Call 'AC_SUBST' for them. At present this assumes GNU compiler
+ warning options, but could be extended to others if necessary.
+
+ This macro caches its results in the 'kpse_cv_warning_cflags', ...
+ variables.
+
+ -- Macro: KPSE_COMPILER_VISIBILITY
+ When using the C or C++ compiler, try to set
+ 'VISIBILITY_C[XX]FLAGS' to flags to hide external symbols. Call
+ 'AC_SUBST' for this variable. At present this only tests for the
+ compiler option '-fvisibility=hidden', but could be extended if
+ necessary.
+
+ This macro caches its results in the 'kpse_cv_visibility_cflags' or
+ 'kpse_cv_visibility_cxxflags' variable.
+
+ -- Macro: KPSE_CXX_HACK
+ Provide the configure option '--enable-cxx-runtime-hack'. If
+ enabled and when using 'g++', try to statically link with
+ 'libstdc++', notably improving portability of the resulting binary.
+
+ This macro caches its result in the 'kpse_cv_cxx_hack' variable.
+
+6.3.4 Macros for libraries
+--------------------------
+
+One macro for a library check:
+
+ -- Macro: KPSE_LARGEFILE (VARIABLE, [EXTRA-DEFINE])
+ Call 'AC_SYS_LARGEFILE' and 'AC_FUNC_FSEEKO' and append suitable
+ '-D' flags (optionally including '-DEXTRA-DEFINE') to VARIABLE.
+
+6.3.5 Macros for library and header flags
+-----------------------------------------
+
+Each library module 'libs/LIB' or 'texk/LIB' is supplemented by a macro
+'KPSE_LIB_FLAGS' (all uppercase) that provides make variables for that
+library. E.g., for 'libs/libpng':
+
+ -- Macro: KPSE_LIBPNG_FLAGS
+ Provide the configure option '--with-system-libpng'. Set and
+ 'AC_SUBST' 'make' variables for modules using this library (either
+ an installed version or from the TeX Live tree):
+
+ 'LIBPNG_INCLUDES' for use in 'CPPFLAGS',
+ 'LIBPNG_LIBS' for use in 'LDADD',
+ 'LIBPNG_DEPEND' for use as a Makefile dependency,
+ 'LIBPNG_RULE' for the 'make' rules to rebuild the library.
+
+ -- Macro: KPSE_ADD_FLAGS (NAME)
+ Temporarily extend 'CPPFLAGS' and 'LIBS' with the values required
+ for the library module 'NAME'.
+
+ -- Macro: KPSE_RESTORE_FLAGS
+ Restore 'CPPFLAGS' and 'LIBS' to their original values.
+
+ As an example, the 'configure.ac' file for a hypothetical program
+'utils/foo' using 'libpng', and hence 'zlib', would contain
+ KPSE_ZLIB_FLAGS
+ KPSE_LIBPNG_FLAGS
+
+and its 'Makefile.am' would be along these lines:
+ bin_PROGRAMS = foo
+ AM_CPPFLAGS = ${LIBPNG_INCLUDES} ${ZLIB_INCLUDES}
+ foo_LDADD = ${LIBPNG_LIBS} ${ZLIB_LIBS}
+ foo_DEPENDENCIES = ${ZLIB_DEPEND} ${LIBPNG_DEPEND}
+ ## Rebuild libz
+ @ZLIB_RULE@
+ ## Rebuild libpng
+ @LIBPNG_RULE@
+
+ If it were necessary to examine whether certain 'zlib' or 'libpng'
+features were available, 'configure.ac' should be continued this way:
+ KPSE_ADD_FLAGS([zlib])
+ ... # tests for 'zlib' features, if any
+ KPSE_ADD_FLAGS([libpng])
+ ... # tests for 'libpng' features
+ KPSE_RESTORE_FLAGS # restore 'CPPFLAGS' and 'LIBS'
+
+6.3.6 Macros for Windows
+------------------------
+
+Windows differs in several aspects from Unix-like systems, many of them
+due to the lack of symbolic links.
+
+ -- Macro: KPSE_CHECK_WIN32
+ Check if compiling for a Windows system. The result is either 'no'
+ for Unix-like systems (including Cygwin), 'mingw32' for Windows
+ with GCC, or 'native' for Windows with MSVC. The result is cached
+ in the 'kpse_cv_have_win32' variable.
+
+ -- Macro: KPSE_COND_WIN32
+ Call 'KPSE_CHECK_WIN32' and define the Automake conditional 'WIN32'
+ ('true' if the value of 'kpse_cv_have_win32' is not 'no').
+
+ -- Macro: KPSE_COND_MINGW32
+ Call 'KPSE_COND_WIN32' and define the Automake conditional
+ 'MINGW32' ('true' if the value of 'kpse_cv_have_win32' is
+ 'mingw32').
+
+ -- Macro: KPSE_COND_WIN32_WRAP
+ Call 'KPSE_COND_WIN32' and define the Automake conditional
+ 'WIN32_WRAP' ('true' if the standard Windows wrapper
+ ('texk/texlive/w32_wrapper/runscript.exe') exists. This wrapper is
+ used on Windows instead of symlinks for the "linked scripts" (*note
+ Linked scripts::).
+
+ -- Macro: KPSE_WIN32_CALL
+ Call 'KPSE_COND_WIN32' and check if the file
+ 'texk/texlive/w32_wrapper/callexe.c' exists; if it does, create a
+ symlink in the build tree. Compiling 'callexe.c' with
+ '-DEXEPROG='"FOO.exe"'' and installing 'callexe.exe' as 'BAR.exe'
+ is used on Windows instead of a symlink 'BAR->FOO' for Unix-like
+ systems.
+
+6.4 Library modules
+===================
+
+Here we discuss some specifics for a few of the libraries in TL, both
+for the details themselves, and as a way of illuminating the general
+structure and variation.
+
+6.4.1 The 'png' library in 'libs/libpng'
+----------------------------------------
+
+The "generic" 'png' library uses the source tree in the subdirectory
+'libpng-src/', with all modifications for TL recorded in 'TLpatches/*'.
+The 'configure.ac' fragment 'ac/withenable.ac' contains
+
+ KPSE_WITH_LIB([libpng], [zlib])
+
+to specify the module name and indicate the dependency on 'zlib'. A
+third literal argument ''tree'' would specify that the library from the
+TeX Live tree cannot be replaced by a system version. That not being
+the case here, a second fragment 'ac/libpng.ac' contains
+
+ KPSE_TRY_LIB([libpng],
+ [#include <png.h>],
+ [png_structp png; png_voidp io; png_rw_ptr fn;
+ png_set_read_fn(png, io, fn);])
+
+thus providing the simple C code
+
+ #include <png.h>
+ int main ()
+ { png_structp png; png_voidp io; png_rw_ptr fn;
+ png_set_read_fn(png, io, fn);
+ return 0; }
+
+which Autoconf uses to verify the usability of a system version with C
+code. The analogous macro 'KPSE_TRY_LIBXX' would check using C++.
+These fragments are included by the 'configure.ac' at the top level of
+TL ('Build/source/configure.ac').
+
+ For this library, like many other modules, a proxy build system for
+TL is used, consisting of our own 'configure.ac', 'Makefile.am',
+'include/Makefile.am'; the distributed build system is not used.
+(Consequently, a few generated files and auxiliary scripts are removed
+from the distributed source tree.)
+
+ The public headers 'png.h', 'pngconf.h', and 'pnglibconf.h' are
+"installed" (as symlinks) under 'include/' in the build tree exactly as
+they are for a system version under, e.g., '/usr/include/'.
+
+ The module is supplemented by the file 'm4/kpse-libpng-flags.m4' that
+defines the M4 macro 'KPSE_LIBPNG_FLAGS' used by all modules depending
+on this library in their 'configure.ac' to generate the 'make' variables
+'LIBPNG_INCLUDES' for use in 'CPPFLAGS', 'LIBPNG_LIBS' for use in
+'LDADD', 'LIBPNG_DEPEND' for use as dependencies, and 'LIBPNG_RULE' for
+the 'make' rules to rebuild the library.
+
+ 'm4/kpse-libpng-flags.m4' also supplies the configure option
+'--with-system-libpng', which then uses 'pkg-config' to determine the
+flags required for the system library.
+
+6.4.2 The 'zlib' library in 'libs/zlib'
+---------------------------------------
+
+This generic library is very much analogous to 'libpng', but without the
+dependency on any other library. The file 'm4/kpse-zlib-flags.m4'
+supplies the configure option '--with-system-zlib', as well as
+'--with-zlib-includes' and '--with-zlib-libdir' to specify non-standard
+locations of the 'zlib' headers and/or library.
+
+6.4.3 The 'freetype' library in 'libs/freetype2'
+------------------------------------------------
+
+This module uses a wrapper build system. In contrast to the proxy build
+described earlier, the wrapper build has an almost trivial
+'configure.ac' and a 'Makefile.am' which invokes the 'configure' and
+'make' in the distributed source, followed by 'make install' with the TL
+build tree as destination. In other words, this actually uses the build
+system provided by upstream (possibly patched).
+
+ The flags required for the system library are obtained through
+'freetype-config'.
+
+6.4.4 The 'kpathsea' library in 'texk/kpathsea'
+-----------------------------------------------
+
+This is one of the TeX-specific libraries that are maintained as part of
+TeX Live (*note (kpathsea)::); the other is 'ptexenc'. These TeX
+libraries are Libtool libraries (static and/or shared) and are installed
+by 'make install' together with the programs. They are, however, not
+part of the TL DVD as distributed by TeX user groups, and have never
+been officially released for standalone use.
+
+ It is possible, and probably useful for distro builds (*note Distro
+builds::), to specify the configure option '--with-system-kpathsea' in
+order to use a system version of the library. Programs outside the TL
+tree should use 'pkg-config' for the required flags.
+
+ In addition to 'kpathsea/ac/withenable.ac' and
+'kpathsea/ac/kpathsea.ac' here there is a third fragment
+'kpathsea.ac/mktex.ac', included by both 'withenable.ac' and
+'configure.ac', which supplies configure options such as
+'--enable-mktextfm-default'. These determine the compile time default
+of whether or not to run 'mktextfm' (and similar) to generate a missing
+'.tfm' (or whatever) file. In any case, however, the command line
+options '-mktex=tfm' or '-no-mktex=tfm' for the TeX-like engines
+override this default.
+
+6.5 Program modules
+===================
+
+As with libraries (*note Library modules::), here we discuss the details
+for a few of the programs in TL.
+
+6.5.1 The 't1utils' package in 'utils/t1utils'
+----------------------------------------------
+
+Here we use the distributed source tree 't1utils-src' with modifications
+documented in 'TLpatches/*' and a proxy build system consisting of
+'configure.ac' and 'Makefile.am'. The fragment 'ac/withenable.ac'
+contains
+
+ KPSE_ENABLE_PROG([t1utils])
+
+specifying the module name without any dependencies, and supplies the
+configure option '--disable-t1utils'.
+
+6.5.2 The 'xindy' package in 'utils/xindy'
+------------------------------------------
+
+This module uses the distributed source tree 'xindy-src/' with
+modifications documented in 'TLpatches/*', and a wrapper 'configure.ac'
+and 'Makefile.am' that descends into 'xindy-src'.
+
+ The 'xindy' build requires a 'make' that supports a 'VPATH' build,
+can handle all targets, and do not refer to '${top_srcdir}' or
+'${top_builddir}'. The fragment 'xindy/ac/withenable.ac' contains
+
+ KPSE_ENABLE_PROG([xindy], , [disable])
+ m4_include(kpse_TL[utils/xindy/ac/xindy.ac])
+ m4_include(kpse_TL[utils/xindy/ac/clisp.ac])
+
+where 'disable' in the third argument indicates that 'xindy' is only
+built if explicitly enabled by the user with 'configure --enable-xindy'
+(the need for 'clisp' makes it too painful to enable by default).
+
+ The additional fragments 'ac/xindy.ac' and 'ac/clisp.ac' specify more
+'configure' options to be seen at the top level, with 'ac/xindy.ac' also
+included by 'configure.ac'.
+
+6.5.3 The 'xdvik' package in 'texk/xdvik'
+-----------------------------------------
+
+This package is maintained as part of the TeX Live tree with sources in
+its own directory ('texk/xdvik/'). The fragment
+'xdvik/ac/withenable.ac' contains
+
+ dnl extra_dirs = texk/xdvik/squeeze
+ KPSE_ENABLE_PROG([xdvik], [kpathsea freetype2], [x])
+ m4_include(kpse_TL[texk/xdvik/ac/xdvik.ac])
+
+thus specifying dependencies on the 'kpathsea', 'freetype', and X11
+libraries. The M4 comment (following 'dnl') signals the subsidiary
+'squeeze/configure.ac'. This is needed because the main executable
+'xdvi-bin' (to be installed as, e.g., 'xdvi-xaw') is for the 'host'
+system whereas the auxiliary program 'squeeze/squeeze' has to run on the
+'build' system; in a cross compilation, these differ.
+
+ The additional fragment 'ac/xdvik.ac' is also included by
+'configure.ac' and supplies the configure option '--with-xdvi-x-toolkit'
+also seen at the top level.
+
+6.5.4 The subdirectory 'utils/asymptote'
+----------------------------------------
+
+This subdirectory contains the sources for 'asy' and 'xasy' but due to
+its complexity and prerequisites (e.g., OpenGL) it is not part of the TL
+build system. These programs must be built and installed independently,
+but are included on the TL DVD together with their support files. See
+<https://tug.org/build.html#asymptote>.
+
+6.6 Extending TeX Live
+======================
+
+This section outlines the basic process for adding new packages to the
+TL build system.
+
+ In any case, a new package directory 'foo' should contain the
+original sources, modified only with changes necessary for TL, in
+'foo/foo-src'. The changes should be documented in 'foo/TLpatches/*',
+and also be submitted upstream whenever reasonable. In addition, 'foo/'
+will need the usual Automake build-related files ('configure.ac',
+'Makefile.am', etc. Please maintain 'foo/ChangeLog' for all TL changes.
+
+6.6.1 Adding a new program module
+---------------------------------
+
+A TeX-specific program module in a subdirectory 'texk/PROG' may use the
+TeX-specific libraries and is included by adding its name 'PROG' to the
+M4 list 'kpse_texk_pkgs' defined in 'm4/kpse-pkgs.m4'.
+
+ A generic program module in a subdirectory 'utils/PROG' must not use
+the TeX-specific libraries and is included by adding its name 'PROG' to
+the M4 list 'kpse_utils_pkgs' in 'm4/kpse-pkgs.m4'.
+
+ In either case, the subdirectory 'texk/PROG' or 'utils/PROG' must
+provide a fragment 'ac/withenable.ac' that contains the M4 macro
+'KPSE_ENABLE_PROG' defined in 'm4/kpse-setup.m4' with 'PROG' as the
+mandatory first argument and three optional arguments:
+
+ 1. a list of required libraries from the TL tree;
+
+ 2. a list of options: 'disable' if this module is not to be built
+ without the configure option '--enable-PROG', 'native' if cross
+ compilation is not possible, 'x' if the program requires X11
+ libraries;
+
+ 3. a comment added to the help text for the 'configure' option
+ '--enable-PROG' or '--disable-PROG'.
+
+ If the module requires specific 'configure' options to be seen at the
+top level, they should be defined in an additional fragment 'ac/PROG.ac'
+included from 'ac/withenable.ac' and 'configure.ac'.
+
+ Usually, the new program is maintained somewhere outside of TeX Live.
+In that case, as above, we put the upstream sources into a subdirectory
+'PROG-src' (e.g., 'utils/newprog/newprog-src'). We do not typically run
+'configure' in this original '...-src' directory, but only in our own
+directory; but we do compile using the source files in '...-src'.
+
+ So, to summarize the files that we must (usually) create:
+
+'ac/withenable.ac'
+ The 'KPSE_ENABLE_PROG' call just explained.
+
+'configure.ac'
+'Makefile.am'
+ By merging the contents of the original 'configure.ac' (if
+ provided) and a comparable program already in TL. There is no magic
+ recipe, it's necessary to think about needs to be done in the
+ original vs. in TeX Live.
+
+'TLpatches/TL-Changes'
+ Actions taken after getting the original source tree; typically
+ removal of derived or unused common files.
+
+'TLpatches/patch-...'
+ If any changes are needed to the original sources, record the
+ patches here so they can be applied next time. And send them
+ upstream so that perhaps they won't have to be.
+
+'ChangeLog'
+ Record all TL-specific changes, now and in the future.
+
+ Then, run GNU 'autoreconf' in the new directory (*note Build system
+tools::). After that works, 'svn add' the necessary files, including
+the generated 'Makefile.in aclocal.m4 configure', and 'svn:ignore' the
+Automake cache 'autom4te.cache'. (This is so people checking out the TL
+source tree do not have to run any autotools, but can simply run
+'configure'.)
+
+ Then, run the TL tool 'reautoconf' in the top-level TL 'source/'
+directory, to incorporate the new program into the build tree.
+
+ Then, run (and rerun) a build until the program compiles and tests
+successfully, probably involving rerunning autoreconf in the source
+directory, 'make' in the build directory, etc.
+
+ After final success, don't forget to commit.
+
+6.6.2 Adding a new generic library module
+-----------------------------------------
+
+A generic library module in a subdirectory 'libs/LIB' must not depend on
+TeX-specific libraries, by definition. It is included by adding its
+name 'LIB' to the M4 macro 'kpse_libs_pkgs' in 'm4/kpse-pkgs.m4'--before
+any other libraries from the TeX Live tree on which it depends.
+
+ As with program modules, the subdirectory 'libs/LIB' must contain the
+sources and build system for the library (and any installable support
+programs) and a fragment 'ac/withenable.ac' that contains the M4 macro
+'KPSE_WITH_LIB' defined in 'm4/kpse-setup.m4' with 'LIB' as the
+mandatory first argument and two optional arguments: a list of required
+libraries from the TL tree, and a list of options: for libraries,
+currently there is only one--specify 'tree' if this library cannot be
+replaced by a system version.
+
+ If a system version can be used, a second fragment 'ac/LIB.ac' is
+needed, containing the M4 macro 'KPSE_TRY_LIB' (or 'KPSE_TRY_LIBXX')
+with 'LIB' as the mandatory first argument and two additional arguments
+for the Autoconf macro 'AC_LANG_PROGRAM' used to compile and link a
+small C (or C++) program as sanity check for using the system library.
+
+ In addition a file 'm4/kpse-LIB-flags' (at the top level) must define
+the M4 macro 'KPSE_LIB_FLAGS' (all uppercase) setting up the 'make'
+variables 'LIB_INCLUDES', 'LIB_LIBS', 'LIB_DEPEND', and 'LIB_RULE' with
+the values required for 'CPPFLAGS', 'LDADD', dependencies, and a
+(multi-line) 'make' rule to rebuild the library when necessary. All of
+that is needed for the library from the TL tree and, if supported, for a
+system version.
+
+ If a system library is allowed, 'KPSE_LIB_FLAGS' also provides the
+configure option '--with-system-LIB' and uses the additional M4 macro
+'KPSE_LIB_SYSTEM_FLAGS' to generate the 'make' variables for a system
+library. In addition, the definition of the M4 macro
+'KPSE_ALL_SYSTEM_FLAGS' in 'm4/kpse-pkgs.m4' must be extended by the
+line:
+ 'AC_REQUIRE([KPSE_LIB_SYSTEM_FLAGS])'
+
+6.6.3 Adding a new TeX-specific library module
+----------------------------------------------
+
+A TeX-specific library module in a subdirectory 'texk/LIB' may depend on
+other TeX-specific libraries but must not depend on any generic library
+from the TL tree. It is included in the same general ways as a generic
+library (see the previous section), with these modifications:
+
+ * The library name 'LIB' is added to the M4 macro
+ 'kpse_texlibs_pkgs', which is also in 'm4/kpse-pkgs.m4'.
+
+ * The fragment 'ac/withenable.ac' must use 'KPSE_WITH_TEXLIB'.
+