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+OPM Build System
+================
+
+This is the documentation for the build system used in various OPM modules.
+In the following, `xxx` is used as a placeholder for the project name (e.g.
+"core").
+
+Unlike traditional CMake files which is highly imperative, OPM projects
+sets up declarative lists of prerequisites and content and rely on convention
+and pre-made modules to do the build. Its goal is to replace but be
+compatible with the old autotools-based system.
+
+## Terminology
+
+In the build system to following abstract locations are referred to:
+
+<table><thead><tr><th>Location<th>Description<tbody>
+<tr>
+<td>	Source tree
+<td>
+This is where the source files are located. Usually this directory is created
+by a `git clone`. You edit files in this directory. The build system on the
+other hand will never touch these files; they could be read-only for that
+matter. It should be located on a disk that is backed up. The source trees
+for various OPM modules should be siblings to eachother.
+
+<tr>
+<td>	Build tree
+<td>
+This is where you do `make` (or `ninja`), and the compiler/linker will put
+its output here. It may be the same directory as the source tree (which is
+then called an "in-tree build"). However, it is recommended that you keep
+it separate. Do `make clean && make distclean` to remove all files that
+are created by the build (if you put it in the source directory).
+You don't need to backup these files (since they can be generated from the
+source); instead this directory should be located somewhere with fast
+write access. The build trees for various OPM modules should be siblings
+(unless they are subdirectories in their source trees).
+
+<tr>
+<td>	Installation tree
+<td>
+This is where the build system will put all the final libraries and headers
+when running `make install`.
+You can specify another location for the installation tree by setting the
+CMake variable `CMAKE_INSTALL_PREFIX` on the command line (or use `--prefix=`
+with the configure script). Notice that the portion of this path which
+will become the new filesystem root should be specified with the environment
+variable `DESTDIR`.
+
+</table>
+
+## Use Cases
+
+This section lists some common use cases for adding new code to a project
+with respect to the build system, and lists the steps that must be undertaken
+to do the necessary modifications.
+
+### Adding a Translation Unit
+
+1. Put the file in a sub-directory of `opm/xxx`.
+
+2. Add the file name to the `MAIN_SOURCE_FILES` list in `CMakeLists_files.txt`.
+   Please keep this list sorted.
+
+3. If you are adding new interfaces that will be used by client code, add the
+   header to the `PUBLIC_HEADER_FILES`. Note that any `_impl` headers containing
+   template implementations must also be included.
+
+### Adding a Prerequisite
+
+1. Add the name of the prerequisite module to the `opm-xxx_DEPS` list in the file
+   `cmake/Modules/opm-xxx-prereqs.cmake`, where xxx is a placeholder for the module
+   name of your CMake project.
+
+2. If you need any CMake configuration defines available in your public _headers_,
+   add these to the `opm-xxx_CONFIG_VAR` list in the same file. Please refrain
+   from this practice as it imposes a requirement on the clients of your code to
+   gather the same configuration information and make it available in the units
+   which uses your headers.
+
+### Adding a Unit Test
+
+1. Put the source code in a single translation unit in directory `tests`. The
+   name of this unit should start with `test_`.
+
+2. Put any datafiles this code rely on in the same directory. The code should
+   assume that such datafiles are available in the current directory the program
+   is running from. The code should not write to these files, but rather make
+   a copy if it needs to modify them.
+
+3. Add the file name to the `TEST_SOURCE_FILES` list in `CMakeLists_files.txt`.
+
+4. Add the datafiles to the `TEST_DATA_FILES` list in the same files. The
+   files will be copied from the source tree into the target tree.
+
+### Adding a New Utility Program
+
+1. Put the source code of the utility in the `examples` directory.
+
+2. Add the name of the translation unit to the `PROGRAM_SOURCE_FILES` list
+   in `CMakeLists_files.txt`.
+   
+### Creating a New Module
+
+1. Copy the directory `cmake/` and all sub-directories from opm-core. This
+   directory contains the common build system, and should ideally be identical
+   across OPM projects. Also copy the file `configure` in the project root.
+
+2. Create project-specific files using those from another project as a template.
+   The list of project specific files is in the section
+   [Modules Reference](#project-specific-files) below.
+
+3. Create a new file `cmake/Modules/opm-xxx-prereqs.cmake`, using one of the
+   existing ones as a template.
+
+4. Optionally, create a new file `cmake/Modules/Findopm-xxx.cmake`, using one
+   of the existing ones as a template.
+
+## Options
+
+These options regulate the behaviour of the build system. In addition to these
+options, you can also set standard CMake options, or options for the
+prerequisites, which is not documented here. If you run the configure script
+with the `--help` option, it will print a text of what the options are called
+when using the autotools-compatible wrapper.
+
+<table><thead><tr><th>Option<th>Description<tbody>
+<tr>
+<td>	BUILD_EXAMPLES
+<td>
+Include the examples when doing a build. Whenever you change something
+in the library, however small, all the examples will also be rebuilt.
+Default is ON.
+
+<tr>
+<td>	BUILD_TESTING
+<td>
+Include the unit tests when doing a build. Whenever you change something
+in the library, however small, all the unit tests will also be rebuilt.
+Default is ON.
+
+<tr>
+<td>	PRECOMPILE_HEADERS
+<td>
+Precompile common headers into a binary blob which is loaded on further
+compilations. If your compiler supports this, it usually reduces build
+time. It does not affect the running time of the code. Default is OFF.
+
+<tr>
+<td>	SIBLING_SEARCH
+<td>
+Search for OPM/DUNE prerequisites in sibling directories of the build
+tree. Default is ON.
+
+<tr>
+<td>	SUITESPARSE_USE_STATIC
+<td>
+Link SuiteSparse/UMFPack statically. Using this option will enable you
+to build an executable which has no external dependencies. The default
+is to use shared libraries if those are available.
+
+<tr>
+<td>	SYSTEM_DEBUG
+<td>
+Put debug symbols in the system debug directory (`/usr/lib/debug`) as
+this seems to be the only place which is searched by default by GDB.
+Default is OFF, as it requires that you have write access to that
+directory. Note that if you are doing a system installation (set
+CMAKE_INSTALL_PREFIX=/usr), then the libraries will be put in this
+location irregardless of this option.
+
+<tr>
+<td>	USE_MPI
+<td>
+Enable the code to use MPI for parallelization. Default is OFF.
+Note: It is important that OPM and DUNE modules is either all
+compiled with MPI support or that none is. The build system will
+attempt to recognize inconsistencies.
+
+<tr>
+<td>	USE_OPENMP
+<td>
+Enable the code to use OpenMP for parallelization. Default is ON.
+
+<tr>
+<td>	USE_RUNPATH
+<td>
+Remember the directories from where the prerequisites were found
+when building. Default is ON, which enables you to run without
+setting PATH all over the place in your build directories. When
+creating an installation package, this should be set off.
+
+<tr>
+<td>	USE_UNDERSCORING
+<td>
+Assume that Fortran externals have an underscore suffix instead
+of checking this with an actual compiler. If you set this option,
+you can use Fortran libraries (notably BLAS and LAPACK) without
+having a Fortran compiler installed. The default is OFF.
+
+<tr>
+<td>	USE_VERSIONED_DIR
+<td>
+Put libraries in a directory which includes the label of the project,
+e.g. `/usr/lib/opm-core/2013.10`. Default is OFF.
+
+<tr>
+<td>	WITH_NATIVE
+<td>
+Optimize for the instruction set of the build machine. This is
+a good idea if you are building the library on the same machine
+as you will be using the library. Default is ON.
+
+<tr>
+<td>	WHOLE_PROG_OPTIM
+<td>
+Perform an extra round of optimization when linking the program.
+(Usually the compiler only optimizes within the translation unit).
+If your compiler supports this, it usually leads to a faster runtime.
+Default is OFF.
+
+</table>
+   
+## Modules Reference
+
+### Project-specific Files
+
+All of these files are in the project root, except for `opm-xxx.m4`
+which is in the `m4` directory. (`dunecontrol` always adds this
+subdirectory for all the prerequisites listed in `dune.module`, to the
+search path).
+
+<table><thead><tr><th>File<th>Description<tbody>
+<tr>
+<td>	CMakeLists.txt
+<td>
+Project-specific customizations to the build, such as filtering out source
+files based on the availability of prerequisites, or adding configuration
+variables only the implementation depends on.
+Prefer to do customizations in the hooks available to this file rather than
+adding ad-hoc code to the build system itself, to keep the `cmake/` directory
+unified across projects.
+
+<tr>
+<td>	CMakeLists_files.txt
+<td>
+List of all compilation modules in the project, test cases and public
+headers that should be installed in the distribution package. The contents
+of these lists are distributed to project-specific variables by the build
+system.
+
+<tr>
+<td>	CTestConfig.cmake
+<td>
+Settings for submitting result of tests to CDash. The default is setup
+to submit to [the official CDash panel](http://www.opm-project.org/CDash/)
+and does not need to be changed if your module has a panel there.
+
+<tr>
+<td>	dune.module
+<td>
+Information about the project such as name, release label, link version
+and maintainer. Also specify dependencies to other OPM/DUNE-projects so
+that dunecontrol can build in correct order. (Note that the full list of
+dependencies is taken from opm-xxx-prereqs.cmake and not from here).
+Since this file must be present before the build starts (for dunecontrol),
+the version information is kept here.
+
+<tr>
+<td>	opm_xxx.m4
+<td>
+Tell the generic opm.m4 module which name it should request pkg-config
+for. This module is used by autotools-projects which link to OPM.
+Notice that dashes is replaced by underscore in the filename to be
+compatible with M4. (The actual name of the file doesn't matter to the
+autotools build system). The contents of this file is mostly boiler-plate
+where the names need to be changed to the project in question. (The
+DUNE build system assumes the presence of macros based on the project
+name).
+	
+</table>
+
+### Project Modules
+
+These modules contains the dependency information for this project, so
+the build system can set up the prerequisite list correctly and probe
+for other modules automatically. (This replaces hard-coded calls to
+find_library in the CMakeLists.txt file).
+
+<table><thead><tr><th>File (.cmake)<th>Description<tbody>
+<tr>
+<td>	xxx-prereqs
+<td>
+List prerequisite modules and defines used in public headers. Each module
+must have such a "declaration", and this must be made available to every
+other projects as well (which is why this is located in `cmake/Modules`).
+
+<tr>
+<td>	Findxxx
+<td>
+CMake modules which locates module `xxx` in the system directories. As
+the `opm-xxx-config.cmake` is made available together with the libraries
+and headers, these modules are not really needed (for OPM modules).
+
+</table>
+
+### Generated Files
+
+These files are generated by the build system and exists in the _build_ tree,
+not in the source tree. They are documented here to make developers aware of
+their role in the build system.
+
+<table><thead><tr><th>File<th>Description<tbody>
+<tr>
+<td>	config.h
+<td>
+Settings variables which the build system has configured and make available
+to the source code. This file is **not** installed amongst the headers, so
+you should never include this in a public header, even if you need the value
+in one of these variables. Instead, you must rely on the client code to
+configure this variable for you.
+
+<tr>
+<td>	opm-xxx.pc
+<td>
+pkg-config information file to locate the **build** tree. This is used by
+the autotools build files, but can also be handy when manually building
+small test programs for which you don't generate an own build system.
+
+<tr>
+<td>	opm-xxx-config.cmake
+<td>
+CMake information file to locate the **build** tree. This file is imported
+when this project is set up as a prerequisite.
+
+<tr>
+<td>	opm-xxx-install.pc
+<td>
+pkg-config information file to locate the **installation** tree. It is
+the same as `opm-xxx.pc` except that the paths are switched. When the
+project is installed, this file is installed instead (under `lib/pkgconfig`
+relative to the installation root). This directory should hence be put
+in the search path to pkg-config to use the installed package. Before
+installation, this file is worthless and should not be included, because
+it does not refer to the build tree at all. (Be careful not to mix
+the build and the installation tree).
+Notice that the build system will forward a bunch of public definitions
+which should be available to compile code referring to this library.
+
+<tr>
+<td>	opm-xxx-install.cmake
+<td>
+CMake information file to locate the **installation** tree. It is the
+same as `opm-xxx-config.cmake` except that the paths are switched. When
+the project is installed, this file is installed instead (under `share/cmake`
+relative to the installation root).
+
+<tr>
+<td>	opm-xxx-config-version.cmake
+<td>
+CMake wants to include this into the build _before_ it is determined whether
+the library was found successfully (depending on the version number perhaps),
+so this information is put in its own file. Since it is the same for the
+build tree and the installation tree, it is shared in both those locations.
+
+</table>
+
+### Utility Modules
+
+These modules consists of useful routines which is not OPM-specific and
+that could be used in any projects. They don't depend on any other parts
+of the build system.
+
+<table><thead><tr><th>File (.cmake)<th>Description<tbody><tr>
+<td>	AddOptions
+<td>
+Functions to add options to compiler command line (e.g. 'CXXFLAGS').
+This macro can add options to more than one language and/or configuration
+at a time, and also automatically removes duplicates.
+
+<tr>
+<td>	ConfigVars
+<td>
+Functions to write values of selected variables to `config.h`. The
+advantage of using this compared to a template file, is that other
+modules can add their own variables to be written (a project doesn't
+need to know which variables a prerequisite wants to have in config.h).
+
+<tr>
+<td>	DuneCompat
+<td>
+Modify `Makefile` so dunecontrol can infer source directory from it.
+dunecontrol infers the source location of prerequisites from textual
+analysis of the Makefile in their build tree. (dunecontrol cannot build
+with Ninja anyway, so that is not a problem).
+
+<tr>
+<td>	Duplicates
+<td>
+Functions to remove duplicate values from a list of libraries, which
+must always be done from the beginning in order to link correctly.
+
+<tr>
+<td>	LibtoolArchives
+<td>
+Write .la file which will make libtool find our library. This enables
+users of our library to use libtool even if we did not do so ourselves.
+	
+</table>
+
+### Build System Modules
+
+These are the modules which comprises the OPM-specific parts of the
+build system. The overall flow through the stages of the build is best
+captured by reading through the `OpmLibMain.cmake` module.
+
+<table><thead><tr><th>File (.cmake)<th>Description<tbody>
+<tr>
+<td>	configure
+<td>
+Wrapper script which emulates an autotools front-end, making the build
+system usable with dunecontrol. There is one in the project root directory
+which just forwards everything to the main script in `cmake/Scripts`.
+
+<tr>
+<td>	OpmCompile
+<td>
+Set up a compilation target for the library itself. It is assumed that
+each OPM project build exactly one library file containing all its code.
+The files and compiler options are passed through the project variables
+(see the section [Variables Reference](#variables-reference) below).
+
+<tr>
+<td>	OpmDefaults
+<td>
+If optimization and debugging settings are not given on the command line,
+supply a set of reasonable defaults for the detected platform and
+compiler.
+
+<tr>
+<td>	OpmDistClean
+<td>
+Add a target (`make distclean`) to the build system which can remove the
+build files themselves from the build directory tree.
+
+<tr>
+<td>	OpmDoc
+<td>
+Add target for building documentation, primarily Doxygen class reference
+from the code.
+
+<tr>
+<td>	OpmFiles
+<td>
+Load list of files from `CMakeLists_files.txt` and put into the applicable
+variables.
+
+<tr>
+<td>	OpmGrid
+<td>
+Adds the grid type selection code to config.h which is needed by dune-grid
+if you want to set up a default grid. This is currently not needed by any
+OPM project, and is provided only for porting client projects which previously
+used this functionality from the autotools version.
+
+<tr>
+<td>	OpmInit
+<td>
+Read the version information and project name from `dune.module`.
+
+<tr>
+<td>	OpmInstall
+<td>
+Setup installation of the main library, public headers and debug symbols.
+
+<tr>
+<td>	OpmKnown
+<td>
+Marks as "used" all configuration variables which is used only by some of
+the OPM projects, so they don't generate warnings in the rest of them.
+
+<tr>
+<td>	OpmLibMain
+<td>
+Driver module for the build process. First reads the list of prerequisites
+and options, then set up the compiles and installations.
+
+<tr>
+<td>	OpmProject
+<td>
+Set up pkg-config and CMake information files (see [Generated Files]
+(#generated-files)) for this project, based on configuration.
+
+<tr>
+<td>	OpmSatellites
+<td>
+Build test programs and examples for a library that is bundled in the project.
+</table>
+
+### Wrapper Modules
+
+These modules wrap the CMake `find_library` function and adds the information
+retrieved from the imported prerequisite to module-specific variables, so that
+these can be added to the build in batch afterwards.
+
+<table><thead><tr><th>File (.cmake)<th>Description<tbody>
+<tr>
+<td>	OpmFind
+<td>
+Wrapper around `find_package`. Searches in various locations relative to this
+project as well as in the system directories for a CMake module which can
+locate the package. If it is found, adds the project variables (see
+[Variables Reference](#variables-reference)) for this project into this one,
+for instance include and library directories are added to the compile and link
+command-line for this project.
+
+<tr>
+<td>	OpmPackage
+<td>
+Typical way of finding an OPM package; searches for the header and library,
+and tries to compile a test program. This is the general implementation of
+a CMake find module, and is used to locate those of the prerequisites that
+fits the pattern.
+
+</table>
+
+### Configuration Modules
+
+These are modules for altering the compiler and/or linker option in some way,
+or get information from the system. They are not tied to the OPM projects.
+
+<table><thead><tr><th>File (.cmake)<th>Description<tbody>
+<tr>
+<td>	UseCompVer
+<td>
+Get the version of GCC that is used to compile the project. This is used in
+other modules to enable features that are known to exist/work only in certain
+versions of GCC.
+
+<tr>
+<td>	UseDebugSymbols
+<td>
+Set up the compile to generate debug symbols for the code. This is done also
+if a release build was requested, to be able to do post-mortem debugging of
+production code. (The debug symbols does not inhibit optimization).
+
+<tr>
+<td>	UseDuneVer
+<td>
+Retrieve the version of DUNE which is available.
+
+<tr>
+<td>	UseDynamicBoost
+<td>
+Determine if Boost is linked statically or dynamically (shared). This is
+necessary to know for the unit tests.
+
+<tr>
+<td>	UseFastBuilds
+<td>
+Enable certain techniques which is known to speed up the build itself.
+
+<tr>
+<td>	UseFortranWrappers
+<td>
+Provide a macro for declaration of external symbols which is located in
+Fortran libraries. It is not necessary to have a Fortran compiler present
+to use this macro.
+
+<tr>
+<td>	UseMultiArch
+<td>
+Check if the system uses the multi-arch scheme for organizing libraries
+(currently derivatives of Debian do this).
+
+<tr>
+<td>	UseOnlyNeeded
+<td>
+Only link to libraries which is actually used by the project. Some
+platforms provide "under-linked" libraries (they need other libraries
+but doesn't state so explicitly, but rather imply that the executable
+must link to these itself), and this is also handled.
+
+<tr>
+<td>	UseOpenMP
+<td>
+Add OpenMP features to the build. Since OpenMP is activated by pragmas
+in the code, compiler options instead of libraries are needed.
+
+<tr>
+<td>	UseOptimization
+<td>
+Compile with more extensive optimization that what is the default in
+CMake.
+
+<tr>
+<td>	UsePrecompHeaders
+<td>
+Set up precompiled headers if the project has a `opm/xxx/opm-xxx-pch.hpp`
+header. Due to problems across various compilers, this is currently an
+opt-in feature.
+
+<tr>
+<td>	UseSystemInfo
+<td>
+Retrieve information about the system the build is performed on. This is
+printed in the configuration log and can be helpful to troubleshoot
+problems from error reports.
+
+<tr>
+<td>	UseVCSInfo
+<td>
+Retrieve information about which Git revision is compiled. This is useful
+to figure out which version an error report refers to.
+
+<tr>
+<td>	UseVersion
+<td>
+Add version information for this project into the library binary, making
+it available for query at runtime.
+
+<tr>
+<td>	UseWarnings
+<td>
+Enable a more extensive set of warnings to be reported by the compiler
+than what is the default in CMake.
+
+</table>
+
+## Variables Reference
+
+The build system will setup variables with names of the pattern `xxx_YYY`
+where xxx is the project name (here including the suite; e.g. "opm-core")
+and yyy is the suffix in the list below. The project name is used verbatim,
+i.e. there is no translation of dashes and case ("opm-core" and not "OPM_CORE").
+
+<table><thead><tr><th>Suffix<th>Description<tbody>
+<tr>
+<td>	_DEFINITIONS
+<td>
+Macro defines (of the type `-DFOO`) that needs to be added to the compile
+of translation units contained in this library. This also includes defines
+that must be present to headers which is included by this library.
+
+<tr>
+<td>	_CONFIG_VARS
+<td>
+Defines which should be present in `config.h` of the project which
+includes this library (client code). Only the names of the variables
+are listed here; the actual values must be found by the configuration
+script of the client.
+
+<tr>
+<td>	_CONFIG_IMPL_VARS
+<td>
+Defines which should be present in `config.h` but is only used by
+the internal code of the project itself. Use this list to get
+defines without imposing a requirement on client code to also probe
+for values.
+
+<tr>
+<td>	_INCLUDE_DIR
+<td>
+Directory where the public headers of this project are stored.
+
+<tr>
+<td>	_INCLUDE_DIRS
+<td>
+List of include directories that must be on the compiler search
+path to compile code which uses this project. In addition to the
+headers of this project itself, it also includes the transitive
+closure of paths for all prerequisites as well.
+
+<tr>
+<td>	_LABEL
+<td>
+Currently for OPM projects, this follows a pattern of `YYYY.MM`
+where YYYY is the year of the release and MM is the month. This
+gives information to humans about how up to date this instance
+of the library is (but doesn't provide a way to check for
+compatibility, which is why the VERSION alternatives exist).
+
+<tr>
+<td>	_LIBRARY
+<td>
+Name and path of the binary to link with.
+
+<tr>
+<td>	_LIBRARIES
+<td>
+Full list of the library of both this project, and all its
+prerequisites, that need to be included in the link. I.e. the
+client code should only include the transitive list from its
+immediate prerequisites and not know about the full dependency
+graph.
+
+<tr>
+<td>	_LIBRARY_DIRS
+<td>
+Directories that should be added to the linker search path when
+including this library.
+
+<tr>
+<td>	_LINKER_FLAGS
+<td>
+Flags that must be added to the link when including this library.
+
+<tr>
+<td>	_SOURCES
+<td>
+List of source files contained in this project. This enables libraries
+to be distributed in source form (e.g. CJSON and TinyXML) and linked
+directly into the project.
+
+<tr>
+<td>	_TARGET
+<td>
+Name of the library which is generated by this project. CMake and
+autotools do not like library names which contains dashes, so they
+are stripped out. By using a macro for this we are guaranteed uniform
+translation.
+
+<tr>
+<td>	_VERSION
+<td>
+Textual concatenation of all components of the version number (see below)
+with a dot inbetween. This form of version number can be compared using
+CMake VERSION_{LESS|EQUAL|GREATER} operators. 
+
+<tr>
+<td>	_VERSION_MAJOR
+<td>
+Major version of the library. If the major versions doesn't match, then
+compatibility with existing code cannot be reckoned.
+
+<tr>
+<td>	_VERSION_MINOR
+<td>
+Minor version of the library. Libraries with newer minor version can
+have more features, but should be able to run old code.
+
+<tr>
+<td>	_VERSION_REVISION
+<td>
+Micro version of the library. This number is generally incremented
+whenever bugfixes or performance improvements are made.
+</table>