Help: CPackComponent: Sectioning and rewording

* Insert section and subsection headers (because this is a very long
    doc page)
* In the Introduction, first say that module is included automatically
* Then start with operational definition of components
* Remove duplications
* Also reword the description of the command cpack_add_component

Modules/CPackComponent.cmake

@@ -7,25 +7,32 @@ CPackComponent
 
 Configure components for binary installers and source packages.
 
-Variables concerning CPack Components
+.. only:: html
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-This module handles the component part of :module:`CPack`.
+  .. contents::
 
-For certain kinds of binary installers (especially the graphical installers),
+Introduction
-CPack generates installers that allow users to select individual application
+^^^^^^^^^^^^
-components to install.
+
-The contents of each of the components are identified by the ``COMPONENT``
+This module is automatically included by :module:`CPack`.
-argument of CMake's :command:`install` command.  These components can be
+
+Certain binary installers (especially the graphical installers) generated
+by CPack allow users to select individual application *components* to install.
+This module allows developers to configure the packaging of such components.
+
+Contents is assigned to components by the ``COMPONENT``
+argument of CMake's :command:`install` command.  Components can be
 annotated with user-friendly names and descriptions, inter-component
 dependencies, etc., and grouped in various ways to customize the
-resulting installer.  See the cpack_add_* commands, described below,
+resulting installer, using the commands described below.
-for more information about component-specific installations.
 
-Component-specific installation allows users to select specific sets
+To specify different groupings for different CPack generators use
-of components to install during the install process.  Installation
+a CPACK_PROJECT_CONFIG_FILE.
-components are identified by the ``COMPONENT`` argument of :command:`install`,
+
-and should be further described by the following CPack commands:
+Variables
+^^^^^^^^^
+
+The following variables influence the component-specific packaging:
 
 .. variable:: CPACK_COMPONENTS_ALL
 
@@ -59,16 +66,14 @@ and should be further described by the following CPack commands:
  Specify how components are grouped for multi-package component-aware CPack
  generators.
 
- Some generators like RPM or ARCHIVE family (TGZ, ZIP, ...) generates
+ Some generators like RPM or ARCHIVE (TGZ, ZIP, ...) may generate
- several packages files when asked for component packaging.  They group
+ several packages files when there are components, depending
- the component differently depending on the value of this variable:
+ on the value of this variable:
 
- * ONE_PER_GROUP (default): creates one package file per component group
+ * ONE_PER_GROUP (default): create one package per component group
- * ALL_COMPONENTS_IN_ONE : creates a single package with all (requested) components
+ * IGNORE : create one package per component (ignore the groups)
- * IGNORE : creates one package per component, i.e. IGNORE component group
+ * ALL_COMPONENTS_IN_ONE : create a single package with all requested
-
+   components
- One can specify different grouping for different CPack generator by
- using a CPACK_PROJECT_CONFIG_FILE.
 
 .. variable:: CPACK_COMPONENT_<compName>_DISPLAY_NAME
 
@@ -98,10 +103,15 @@ and should be further described by the following CPack commands:
 
  True if this component is not selected to be installed by default.
 
+Commands
+^^^^^^^^
+
+Add component
+"""""""""""""
+
 .. command:: cpack_add_component
 
-Describes a CPack installation
+Describe an installation component.
-component named by the COMPONENT argument to a CMake INSTALL command.
 
 ::
 
@@ -116,13 +126,11 @@ component named by the COMPONENT argument to a CMake INSTALL command.
                       [ARCHIVE_FILE filename]
                       [PLIST filename])
 
-
+``compname`` is the name of an installation component, as defined by the
-
+``COMPONENT`` argument of one or more CMake :command:`install` commands.
-The cmake_add_component command describes an installation component,
+With the ``cpack_add_component`` command one can set a name, a description,
-which the user can opt to install or remove as part of the graphical
+and other attributes of an installation component.
-installation process.  compname is the name of the component, as
+One can also assign a component to a component group.
-provided to the COMPONENT argument of one or more CMake INSTALL
-commands.
 
 DISPLAY_NAME is the displayed name of the component, used in graphical
 installers to display the component name.  This value can be any
@@ -175,6 +183,9 @@ the component.  See cpack_configure_downloads for more information.
 PLIST gives a filename that is passed to pkgbuild with the
 ``--component-plist`` argument when using the productbuild generator.
 
+Add component group
+"""""""""""""""""""
+
 .. command:: cpack_add_component_group
 
 Describes a group of related CPack installation components.
@@ -223,6 +234,9 @@ single entry.
 BOLD_TITLE indicates that the group title should appear in bold, to
 call the user's attention to the group.
 
+Add installation type
+"""""""""""""""""""""
+
 .. command:: cpack_add_install_type
 
 Add a new installation type containing
@@ -247,6 +261,9 @@ DISPLAY_NAME is the displayed name of the install type, which will
 typically show up in a drop-down box within a graphical installer.
 This value can be any string.
 
+Configure downloads
+"""""""""""""""""""
+
 .. command:: cpack_configure_downloads
 
 Configure CPack to download
@@ -279,8 +296,6 @@ requires the ZipDLL plug-in for NSIS, available at:
 
   http://nsis.sourceforge.net/ZipDLL_plug-in
 
-
-
 On macOS, installers that download components on-the-fly can only
 be built and installed on system using macOS 10.5 or later.