ExternalData: Split documentation into sections

Also explicitly mark functions and variables.

Modules/ExternalData.cmake

@@ -2,8 +2,15 @@
 ExternalData
 ------------
 
+.. only:: html
+
+   .. contents::
+
 Manage data files stored outside source tree
 
+Introduction
+^^^^^^^^^^^^
+
 Use this module to unambiguously reference data files stored outside
 the source tree and fetch them at build time from arbitrary local and
 remote content-addressed locations.  Functions provided by this module
@@ -19,10 +26,13 @@ For example, the argument ``DATA{img.png}`` may be satisfied by either a
 real ``img.png`` file in the current source directory or a ``img.png.md5``
 file containing its MD5 sum.
 
-The ``ExternalData_Expand_Arguments`` function evaluates ``DATA{}``
-references in its arguments and constructs a new list of arguments:
+Module Functions
+^^^^^^^^^^^^^^^^
 
-.. code-block:: cmake
+.. command:: ExternalData_Expand_Arguments
+
+  The ``ExternalData_Expand_Arguments`` function evaluates ``DATA{}``
+  references in its arguments and constructs a new list of arguments::
 
     ExternalData_Expand_Arguments(
       <target>   # Name of data management target
@@ -33,11 +43,11 @@ references in its arguments and constructs a new list of arguments:
   It replaces each ``DATA{}`` reference in an argument with the full path of
   a real data file on disk that will exist after the ``<target>`` builds.
 
+.. command:: ExternalData_Add_Test
+
   The ``ExternalData_Add_Test`` function wraps around the CMake
   :command:`add_test` command but supports ``DATA{}`` references in
-its arguments:
-
-.. code-block:: cmake
+  its arguments::
 
     ExternalData_Add_Test(
       <target>   # Name of data management target
@@ -47,10 +57,10 @@ its arguments:
   It passes its arguments through ``ExternalData_Expand_Arguments`` and then
   invokes the :command:`add_test` command using the results.
 
-The ``ExternalData_Add_Target`` function creates a custom target to
-manage local instances of data files stored externally:
+.. command:: ExternalData_Add_Target
 
-.. code-block:: cmake
+  The ``ExternalData_Add_Target`` function creates a custom target to
+  manage local instances of data files stored externally::
 
     ExternalData_Add_Target(
       <target>   # Name of data management target
@@ -64,6 +74,9 @@ placeholders ``%(algo)`` and ``%(hash)`` in each template.  Data fetch
   rules try each URL template in order by substituting the hash
   algorithm name for ``%(algo)`` and the hash value for ``%(hash)``.
 
+Hash Algorithms
+^^^^^^^^^^^^^^^
+
 The following hash algorithms are supported::
 
  %(algo)     <ext>     Description
@@ -78,7 +91,8 @@ The following hash algorithms are supported::
 Note that the hashes are used only for unique data identification and
 download verification.
 
-Example usage:
+Example Usage
+^^^^^^^^^^^^^
 
 .. code-block:: cmake
 
@@ -98,6 +112,9 @@ replaced by the full path to a real instance of the data file
 such as ``MyInput.png.md5`` then the ``MyData`` target creates a real
 ``MyInput.png`` in the build tree.
 
+Referencing File Series
+^^^^^^^^^^^^^^^^^^^^^^^
+
 The ``DATA{}`` syntax can be told to fetch a file series using the form
 ``DATA{<name>,:}``, where the ``:`` is literal.  If the source tree
 contains a group of files or content links named like a series then a
@@ -126,6 +143,9 @@ Configure series number matching with a regex that matches the
 Note that the ``<suffix>`` of a series does not include a hash-algorithm
 extension.
 
+Referencing Associated Files
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 The ``DATA{}`` syntax can alternatively match files associated with the
 named file and contained in the same directory.  Associated files may
 be specified by options using the syntax
@@ -139,6 +159,9 @@ syntax ``REGEX:<regex>``.  For example, the arguments::
 will pass ``MyInput.mha`` and ``MyFrames00.png`` on the command line but
 ensure that the associated files are present next to them.
 
+Referencing Directories
+^^^^^^^^^^^^^^^^^^^^^^^
+
 The ``DATA{}`` syntax may reference a directory using a trailing slash and
 a list of associated files.  The form ``DATA{<name>/,<opt1>,<opt2>,...}``
 adds rules to fetch any files in the directory that match one of the
@@ -148,7 +171,15 @@ directory on the command line and ensure that the directory contains
 files corresponding to every file or content link in the ``MyDataDir``
 source directory.
 
-The variable ``ExternalData_LINK_CONTENT`` may be set to the name of a
+Module Variables
+^^^^^^^^^^^^^^^^
+
+The following variables configure behavior.  They should be set before
+calling any of the functions provided by this module.
+
+.. variable:: ExternalData_LINK_CONTENT
+
+  The ``ExternalData_LINK_CONTENT`` variable may be set to the name of a
   supported hash algorithm to enable automatic conversion of real data
   files referenced by the ``DATA{}`` syntax into content links.  For each
   such ``<file>`` a content link named ``<file><ext>`` is created.  The
@@ -158,7 +189,9 @@ of URL templates (by means outside the scope of this module).  The
   data fetch rule created for the content link will use the staged
   object if it cannot be found using any URL template.
 
-The variable ``ExternalData_OBJECT_STORES`` may be set to a list of local
+.. variable:: ExternalData_OBJECT_STORES
+
+  The ``ExternalData_OBJECT_STORES`` variable may be set to a list of local
   directories that store objects using the layout ``<dir>/%(algo)/%(hash)``.
   These directories will be searched first for a needed object.  If the
   object is not available in any store then it will be fetched remotely
@@ -166,21 +199,32 @@ using the URL templates and added to the first local store listed.  If
   no stores are specified the default is a location inside the build
   tree.
 
-The variable ``ExternalData_SOURCE_ROOT`` may be set to the highest source
+.. variable:: ExternalData_SOURCE_ROOT
+
+  The ``ExternalData_SOURCE_ROOT`` variable may be set to the highest source
   directory containing any path named by a ``DATA{}`` reference.  The
   default is ``CMAKE_SOURCE_DIR``.  ``ExternalData_SOURCE_ROOT`` and
   ``CMAKE_SOURCE_DIR`` must refer to directories within a single source
   distribution (e.g.  they come together in one tarball).
 
-The variable ``ExternalData_BINARY_ROOT`` may be set to the directory to
+.. variable:: ExternalData_BINARY_ROOT
+
+  The ``ExternalData_BINARY_ROOT`` variable may be set to the directory to
   hold the real data files named by expanded ``DATA{}`` references.  The
   default is ``CMAKE_BINARY_DIR``.  The directory layout will mirror that of
   content links under ``ExternalData_SOURCE_ROOT``.
 
-Variables ``ExternalData_TIMEOUT_INACTIVITY`` and
-``ExternalData_TIMEOUT_ABSOLUTE`` set the download inactivity and absolute
-timeouts, in seconds.  The defaults are 60 seconds and 300 seconds,
-respectively.  Set either timeout to 0 seconds to disable enforcement.
+.. variable:: ExternalData_TIMEOUT_INACTIVITY
+
+  The ``ExternalData_TIMEOUT_INACTIVITY`` variable sets the download
+  inactivity timeout, in seconds, with a default of ``60`` seconds.
+  Set to ``0`` to disable enforcement.
+
+.. variable:: ExternalData_TIMEOUT_ABSOLUTE
+
+  The ``ExternalData_TIMEOUT_ABSOLUTE`` variable sets the download
+  absolute timeout, in seconds, with a default of ``300`` seconds.
+  Set to ``0`` to disable enforcement.
 #]=======================================================================]
 
 #=============================================================================