haiku/docs/user/apidoc.dox

/*
 * Copyright 2007 Haiku Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 *
 * Documentation by: 
 *   Niels Sascha Reedijk <niels.reedijk@gmail.com>
 */

/*!
  \page apidoc Documenting the API
  
  This article explains how to document the API. Its intended audience are the
  Haiku developers who want to document their own classes, and also the members
  of the API Documentation team who want to brush up the documentation.
  
  This document is divided into three sections. \ref formalrequirements
  describes the demands that are made from the markup and spacing of the files.
  \ref commands describes the subset of Doxygen commands the Haiku API
  documentation uses, and which commands are used in which situation. \ref style
  describes the required style and structure of the documentation.
  
  If you are a developer and you want to prepare the first version of the
  documentation for the API documentation team to go over, have a good look at
  the formal requirements and the Doxygen commands. In addition, have a quick
  glance at how to write member and class documentation, since you'll need to
  know which information is mandatory for the documentation. Aspiring members or
  members of the API documentation team should read the third section carefully,
  and should also check out some of the finished documentation to get a good
  grip on the actual tone, style and contents of the documentation.
  
  \section formalrequirements Formal Requirements

  This section describes formal requirements, such as location and naming of
  the files, the header blocks of files, what blocks of documentation look like
  and how to put delimiters to separate different 'blocks' in your source file.
  
  \subsection formalrequirements_location Location of the Documentation Source
  
  Doxygen, the tool that we use to generate the marked up documentation, has an
  ingenious parser that is able to scan through both header and source files
  making it possible to document the API directly in the headers or the source.
  However, the Haiku project have decided not to put the documentation in either
  location, and opt for the third option Doxygen provides: to put the
  documentation into separate files.
  
  \note The reasons to not put the documentation in the header files are
    twofold. First of all, it would add unnecessary cruft to the headers that
    the compiler will needlessly have to parse. File access and speed isn't BeOS
    and Haiku's best quality. The second reason is that the system headers are
    included throughout the tree. It's a waste of electricity to have everybody
    recompile the entire tree if someone fixes a typo in the documentation.
    Likewise, the reason to not put the documentation in the source code is that
    it unnecessarily clutters up that file. By not using direct documentation we
    lose some advantages, like the fact that developers might be inclined to
    update the documentation quicker if they change a method, but as you will
    see we'll have some methods in place to prevent that to a certain extent.
  
  There are a few aspects to the naming and locations of files:
  -# Most important, documentation files \b mirror header files. This not only
    means that they get the same name, but also that the order of the methods,
    variables, functions, etc. will have to be the same.
  -# The root directory of the public API headers is at \c /trunk/headers/os.
    In a similar vein, the root of the documentation files is at
    \c /trunk/src/documentation/haiku_book. The subdirectory structure, or
    the division of kits, will also be replicated.
  -# The name of the files is the same as the base of the header files, with
    the \c dox extension. So \c Something.h becomes \c Something.dox. Note
    the case!
  
  \subsection formalrequirements_headerblock The Header Block
  
  Every documentation file will begin with the header block. It's basically a
  copyright block, with a reference to the author(s) and against which revision 
  the documentation was written.

  \verbatim
/*
 * Copyright 2007 Haiku Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 *
 * Documentation by:
 *  Niels Sascha Reedijk <niels.reedijk@gmail.com>
 * Corresponds to:
 *   /trunk/headers/os/support/String.h  rev 19731
 *   /trunk/src/kits/support/String.cpp  rev 19731
 */
  \endverbatim
  
  The example above has a few elements that you should take note of:
  -# The header is put in a standard C comment, which is enclosed between
    \c /* and \c *\/.
  -# Every line starts with a whitespace and an asterix, followed by another
    space. If the text is part of a category, such as <tt>Documentation 
    by</tt>, put three spaces after the delimiter.
  -# We start with a copyright notice. The first line is empty, then the 
    copyright notice, then the line on \e MIT, followed by an empty line.
  -# Then there is a label <tt>Documentation by:</tt>, which is followed by
    lines with names and email addresses between brackets.
  -# The final part is underneath the label <tt>Corresponds to:</tt>.
    Underneath there is a list of files and their svn revisions that the
    current documentation is known to correspond with.
  -# The header block ends with the \c *\/, where the asterix is aligned with
    the ones above it.
  
  \subsection formalrequirements_blocks Blocks
  
  Blocks are the basic units of documentation for Doxygen. At first it will feel
  like overkill to use blocks, but realize that Doxygen was initially designed
  to operate on header and source files, and then the blocks of documentation
  would be before the definition or declaration of the methods, functions,
  etcetera. Doxygen is used to operating on blocks, and that's why we need to
  reproduce them in our \c dox files.
  
  Blocks should adhere to the following standards:
  -# All blocks open with \c /*! and close with \c * /
  -# The documentation is placed in between these markers.
  -# All the contents in between the markers is indented by two spaces.
  -# The maximum width of the contents between blocks is 80 columns. <em>Try not
    to cross this limit</em>, because it will severely limit readability.
  
  Example:
  \verbatim
/*!
  \fn bool BList::AddItem(void *item)
  \brief Append an item to the list.

  \param item The item to add.
  \retval true The item was appended.
  \retval false Item was not appended, since resizing the list failed.
  \sa AddItem(void *item, int32 index)
*/
  \endverbatim
  
  \note Doxygen also allows the use of single line comments, starting with 
    \c //!, however, we won't use these \b except for group markers, which you
    can read more about in the next section.
  
  \subsection formalrequirements_delimiters Delimiters
  
  Many of the header files in the Haiku API just document one class or one group
  of functions. However, there be a time when you come across a more complex
  header and for the sake of clarity in your \c dox file you want to mark the
  sections. Use the standard delimiter marker for this, which consists of five
  slashes, a space, the title of the section, a space and another five slashes.
  Like this: <tt>///// Global Functions /////</tt>.
  
  \note This is only for the source files and for you as documenter. It will
    not show up in the actual generated documentation!
  
  \section commands Doxygen Commands
  
  This section describes all the Doxygen commands that will be used in the Haiku
  API documentation. As a rule, Doxygen commands start with a backslash (\\) and
  are followed by whitespace (such as a space or a newline), with the exception
  of group markers; this is discussed in more detail later on. The commands can
  be divided into several categories, which are described in the following
  subsections.
  
  \note This section does not discuss which commands you should actually use
    in documentation. See the next section on \ref style
    for that. This section merely explains the different groupings and
    syntaxes of commands.
  
  Most commands accept an argument. Arguments can be one of these three types:
  - \<single_word\> - The argument is a single word.
  - (until the end of the line) - The argument runs until the end of the line.
  - {paragraph} - The argument runs for an entire paragraph. A paragraph is
    ended by an empty line, or if another command that defines a \ref
    commands_sections sections is found. Note that if you use commands that
    work on a paragraph and you split it over multiple lines (because of the
    maximum line width of 80 characters or because it looks better), you will
    have to indent subsequent lines that belong to the paragraph with two more
    spaces, making the total of four. This is to visually distinguish
    paragraphs for other documenters.
  
  \subsection commands_definitions Block Definitions
  
  Because our API documentation is not done in the source, nor in the headers,
  Doxygen needs to be helped with figuring out what the documentation in the
  different blocks actually are about. That's why the first line in a
  documentation block would be one of the following commands:
  
  - \c \\class \<name\> \n
    Tells Doxygen that the following section is going to be on the class as
    specified by \a name.
  - \c \\fn (function declaration) \n
   This block is going to be about the function that corresponds to the given
   declaration. Please note that the declaration is what you find in the source
   file, so if class members are declared, the classname and the scope operator,
   \c ::, are to be added as well. Modifiers such as \c const should be
   included.
  - \c \\var (variable declaration) \n
    This block is going to be about the variable indicated by the declaration.
    This means basically that data members of a class should have the classname
    and the scope operator as well.
  - \c \\typedef (typedef declaration) \n
    This block is going to be about the typedef indicated by the declaration.
    Copy the declaration exactly, including the leading \c typedef keyword.
  - \c \\struct \<name\> \n
    Tells Doxygen the section is going to be on the \c struct indicated by
    \a name. 
  - \c \\def \<name\> \n
    This block is going to be about the \c \#define with the identifier \a name.
  - \c \\page \n
    This block represents a page. See the section on \ref commands_pages for
    detailed information on pages.
  
  \subsection commands_sections Sections in Member Documentation
  
  If you have a look at the output that Doxygen generates, you can see that
  there are recurring sections in the documentation. Documentation that belongs
  to a certain section should be placed after a command that marks the start
  of that section. All the commands take a paragraph as answer. A paragraph
  ends with a whitespace, or with a command that marks a new section. Note that
  this list only shows the syntax of the commands. For the semantics, have a
  look at the next section on style. In member documentation you can use the
  following:
  
  - \c \\brief {brief description} \n
    This is the only \b mandatory section. Every member should have at least
    a brief description. 
  - \c \\param \<parameter-name\> {parameter description} \n
    This section describes a parameter with the name \a parameter-name. The
    parameter name must match the function declaration, since Doxygen will
    check if all the documented parameters exist.
  - \c \\return {description of the return value} \n
    This section describes the return value. This is a totally free form
    paragraph, whereas \c \\retval has a more structured form.
  - \c \\retval \<value\> {description} \n
    This section describes the return value indicated by \a value. 
  - \c \\see {references} \n
    This section contains references to other parts of the documentation.
  
  There are also a number of things that can be used in pages and member
  documentation. See the style section to find out the appropriate situations in
  which to use them.
  
  - \c \\note {text}
  - \c \\attention {text}
  - \c \\warning {text}
  - \c \\remarks {text}
  
  \subsection commands_markup Markup
  
  Sometimes you might require certain text to have a special markup, to make
  words stand out, but also if you want to have example code within the
  documentation you'll need a special markup. Doxygen defines three types of
  commands. There are commands that work on single words, commands that work on
  longer phrases and commands that define blocks. Basically, the single letter
  commands are commands that work on a the next word. If you need to mark
  multiple words or sentences, use the HTML-style commands. Finally, for blocks
  of code or blocks of text that need to be in "typewriter" font, use the block
  commands. Have a look at the following listing:
  
  - \c \\a \n
    Use to refer to parameters or arguments in a running text, for example
    when referring to parameters in method descriptions.
  - <b>Bold text</b>
    - For single words, use \c \\b.
    - For multiple words, enclose between the \c \<b\> and \c \<\\b\> tags.
  - <tt>Typewriter font</tt> \n
    This can be used to refer to constants, or anything that needs to be in
    a monospace, or typewriter, font. There are a few options
    - \c \\c for single words.
    - \c \<tt\> and \c \<\\tt\> for multiple words or phrases
    - The commands \c \\verbatim and \c \\endverbatim. Everything between these
    two commands will be put in a distinct block that stands out from the rest
    of the text.
    - The commands \c \\code and \c \\endcode do the same, but Doxygen will
    parse the contents and try to mark up the code to make it look a little bit
    nicer.
  - <em>Emphasis</em>
    - \c \\e for single words.
    - \c \<em\> and \c \<\\em\> for phrases.
  
  \subsection commands_pages Page Commands
  
  Pages are a very special element of the documentation. They are not 
  associated with any kind of module, such as files or classes, and therefore,
  since they're not members, some of the structuring commands won't work.
  Important to know is that a page is the complete length of the block, so
  dividing it up in subsections by starting new blocks will not work. Instead,
  Doxygen provides some commands to structure text on a page.
  
  First of all, you define a new page by using the \c \\page command. This
  command takes two arguments: a \c \<name\> and <tt>(a title)</tt>. The name
  is the internal identifier that can be used in linking between pages (see
  \ref commands_miscellaneous for \c \\ref). After you've defined the block
  to be a page, you can start writing the contents. 
  
  For more complicated pages,  you might want to divide the page up in sections.
  Use the \c \\section command to define a new section. It takes the same
  arguments as \c \\page, namely the \c \<name\> and the <tt>(title)</tt>. If
  you need a deeper hierarchy you may use \c \\subsection and 
  \c \\subsubsection, again, both with the same syntax. If you need to
  distinguish between sections in subsubsections, you are able to use 
  \c \\paragraph, which takes the same arguments.
  
  \note Before and after each of the commands above, you need to have an empty
    line so as to provide readability. It is not necessary to indent sections
    and subsections more than the normal two spaces, as long as you keep the
    section markers clear.
  
  \warning If you are entering the realm of subsections and sub-subsections,
    think about the nature of your page. Either it needs to be split up into
    multiple pages, or what you're writing is too complex and would be better
    off as a big tutorial on the Haiku website.
  
  If you are creating multiple pages that are related, you will be able to
  structure them in a tree by using the \c \\subpage command. This will rank
  the different pages in a tree structure. It will put a link in the place of
  the command, so you should place it at the top of the parent place and use
  it as an index.
  
  \subsection commands_grouping  Member Grouping Commands
  
  Doxygen makes it possible to group certain members together. It is used
  in the BString class for example, where the members are grouped by what kind
  of operation they perform, such as appending, finding, etc. Defining groups
  is currently not as powerful as it could be, but if you use it inside classes,
  you will be fine if you follow the instructions presented in this section.
  
  \note If you are looking on how to add classes to kits, see
    \ref commands_miscellaneous and have a look at the \c \\ingroup command.
  
  Groups of members are preceded by a block that describes what the group is
  about. You are required to give each group of members at least a name. Have
  a look at the example: 
  
  \verbatim
/*!
  \\name Appending Methods
  
  These methods append things to the object.
*/

//! \@{

... names of the methods ...

//! \@}
  \endverbatim
  
  The block preceding the block opening marker, <tt>//! \@{</tt>, contains a
  \c \\name command and a paragraph that gives a description. The header block 
  can be as long or short as you want, but please don't make it too long. See
  the \ref style section on how to effectively write group headers. The
  members that you want to belong to the group are between the group opening
  and closing markers.
  
  \note Group headers don't have a \c \\brief description.
  
  \subsection commands_miscellaneous Miscellaneous Commands
  
  There are some commands that don't fit into the categories above, but that
  you will end up using every now and then. This section will describe those
  commands.
  
  The first one is \c \\n. This commands sort of belongs to the category of
  markup commands. It basically forces a newline. Because Doxygen parses
  paragraphs as a single contiguous entity, it's not possible to mark up the
  text using carriage returns in the documentation. \c \\n forces a newline in
  the output. So in HTML it will be translated into a \c \<br\\\>.
  
  Sometimes there are some parts of the API that you don't want to be visible.
  Since Doxygen extracts all the public and protected members from a class,
  and virtually every member from a file, you might want to force it to hide
  certain things. If so, use the \c \\internal command. If you place this just
  after the block marker, the command will be hidden from documentation. Any
  further documentation or remarks you put inside the block will not be visible
  in the final documentation. 
  
  Images can be a valuable addition to documentation. To include ones you made,
  use the \c \\image command. It has the following prototype:
  <tt>\\image \<format\> \<file\></tt>. The format is currently fixed at
  \c html. The file refers to the filename relative to the location of the
  documentation file. Any images you want to add should be in the same location
  as the dox file, so only the file name will suffice.
  
  Modules are defined in the main book, and you can add classes to them by
  using the \c \\ingroup command. This commands adds the class to the module
  and groups it on a separate page. At this moment, the group handling has yet
  to be finalised. For now, add the classes to the kit they belong in. In the
  future this might change.
  
  Finally, it is a good idea to link between parts of the documentation. There
  are two commands for that. The first one is \c \\ref, which enable you to refer
  to pages, sections, etc. that you created yourself. The second one is \c \\link 
  which refers to members. The first one is takes one word as an argument, the
  name of the section, and it inserts a link with the name of the title. \c \\link
  is more complex. It should always be accompanied by \c \\endlink. The first
  word between the two commands is the object that is referred to, and the
  rest is the link text. 
  
  \section style Writing Guidelines
  
  This final section will present guidelines for the actual writing of the
  documentation. Both the structure of the documentation, which sections to use
  when, and the style of the writing will be discussed. Before diverging into
  the requirements for file and class descriptions, member descriptions and
  pages, there are some general remarks that apply to all types of
  documentation.
  
  First of all, everything you write should be in <em>proper English 
  sentences</em>. Spelling, grammar, punctuation, make sure you adhere to the
  standards. It also means the following:
  - It means that every sentence should at least have a
    subject and a verb (unless it's an imperative statement).
  - Also use the proper terminology. Remember, you are dealing with C++
    here, which means you should use the right names. So use \b method instead
    of function, and data member instead of variable (where appropriate).
  - Avoid informalism. Avoid constructs like 'if you want to disconnect the 
    object', but rather use 'to disconnect the object'. Avoid familiarisms, or
    jokes.
    
  \remarks It isn't the goal to create dry, legal-style documentation. Just
    try to find a balance. Read through documentation that's already been
    approved to get a hint of what you should be aiming for.
  \remarks If you are having a problem with phrasing certain things, put it
    down in such a way that it says everything it needs to. A proofreader might
    then be able to rephrase it to a better style.
  
  Throughout the documentation you might want to provide hints, warnings or
  remarks that might interrupt the flow of the text, or that need to visually
  stand out from the rest. Doxygen provides commands for paragraphs that
  display remarks, warnings, notes and points of attention. You can use these
  commands in case you meet one or more of the following requirements:
  - The point is for a specific audience, such as beginners in the Haiku API.
    Notes on what to read first, or mistakes that may be made by beginners will
    not be for the entire audience, and such should be separated. These kinds of
    notes should be at the end of blocks.
  - The point needs to visually stand out. This is especially the case with
    remarks, but could also apply for other types.
  - The point is not completely relevant to the text and therefore should be
    separated so that it doesn't interrupt the main flow.
  
  This listing shows which one to use for which situation:
  - \c \\attention
    - Used when the developer is bound to make a mistake, when the API is
      ambiguous. The difference between this and a warning is that warnings warn
      about things that are the developers fault, and attention blocks warn
      about things that might go wrong because of the way the API is structured.
    - Used to warn for abuse of the API that might be caused by the way the
      internals of the system are structured.
  - \c \\warning
    - Used to warn developers about using the API in a certain way. Warnings
      apply especially to new developers that aren't completely familiar with
      the API and that might want to abuse it. For example, the thread safety
      of BString requires a warning.
  - \c \\note
    - Used to place references to other documentation that might not be
      directly related to the text. For example, BLooper will have a direct
      reference to BHandler in the class description, but BMessenger will be
      mentioned in a note because it does not directly influence the use of
      the class.
    - Can also be used for useful hints or notes that somehow need to stand
      out from the rest of the text.
  - \c \\remarks
    - Remarks are small notes that would interrupt the flow of the text. For
      example, if you in a text ignore a certain condition that is so extremely
      rare and uncommon, you can put a remark at the end of the text to tell
      that you have been lying.
    - Remarks interact with the text whereas notes add something unmentioned to
      it.
  
  \subsection style_files File Descriptions
  
  The design of Doxygen makes it very file oriented, and this might come off as
  inconvenient. At the moment, how to actually group the documentation is still
  under debate, but it does not change the requirement that a header needs to
  be documented before the members of that header can be documented. As such,
  the first documentation block in your \c dox file will be the block that
  describes the header. Examples:
  
  \verbatim
/*!
  \file String.h
  \brief Defines the BString class and global operators and functions for 
    handling strings.
*/

/*!
  \file SupportDefs.h
  \brief Defines basic types and definitions for the Haiku API.
*/ 
  \endverbatim
  
  The first statement defines what the block is about, namely the header file.
  The second element is the \c \\brief remark on what it contains. The first
  file defines the BString class and some global operators. You can see that
  reflected in the description. SupportDefs.h does not define classes, but
  rather a range of different functions and defines, so the text refers to that.
  
  \remarks \\brief documentation for files is about what it \e implements, as
    header files are passive (whereas members and functions are active). Thus,
    use the third person form of the verb.
  
  \subsection style_classes Class Descriptions
  
  Classes are the basic building blocks in the Haiku API and as such have
  extensive documentation. This section will go over the actual class
  description. This section will present a list of items you should think about
  when writing the class description. This doesn't mean you'll have to include
  every item, it merely serves as a guiding principle that helps organise your
  thoughts. Have a look at the list:
  
  -# The \c \\brief description is \b obligatory. This description describes
    what it is. For example, BDataIO: "Abstract interface for objects that
    provide read and write access to data." Note that this description is not
    a full sentence, but it does end with a period.
  -# One or more paragraphs that give a broad overview of what the class can
    do. Describe things like what it works on, when you want to use it, what
    advantage it might give over other directly related alternatives. Also
    describe if a class is made to be derived from, and if so, how. Make
    sure that a developer in the first few paragraphs can judge if what he
    wants to do can be done with this class. 
  -# One or more paragraphs that show how this class ties in with the rest
    of the kit or the API. What objects does it work with, how it interacts
    with the servers, etcetera. 
  -# One or more paragraphs that give a concrete example or use case. Keep it
    tidy and self contained. Remember, an example can illustrate better than a
    few paragraphs of text.
  -# End with a list of references to other classes, functions, pages, etc. that
   might be of interest to the reader.
  
  When documenting classes, don't be to exhaustive. Avoid becoming a tutorial
  or a complete guide. This documentation is for reference only. If you want to
  enlighten the reader on bigger subjects, consider writing a separate
  documentation page that connects the different points you want to make.
  
  Also, you don't have to put in any groupings of members in class descriptions.
  If you want to do that, physically divide the members up in groups. Look at
  the \ref commands_grouping for the actual commands, and at \ref style_groups
  for help on writing group headers.
  
  \subsection style_members Members and Functions
  
  Members and functions share the same basic Doxygen syntax, and they can be
  documented in a similar way. That's why this section deals with them together.
  Documenting members is probably the main thing you'll do when writing the
  actual documentation. There are some guidelines as to how, but the actual
  implementation probably differs per class. Keep the following points in mind:
  
  -# To repeat a very important fact, the first line is a \c \\fn line. This
    line needs to match the declaration, which is in the source file. This
    means that for members, also the class name and the scope indicator (::)
    should be present. Also note that this line doesn't have to adhere to
    the 80 column width limit.
  -# The first command is always the \c \\brief command. Give a short and
    clear description. The description starts with a capital letter and ends
    with a dot. Don't write the description saying what the method does,
    like "Starts the timer", but rather as what it will do: "Start the timer."
  -# If the brief description doesn't cover all of what the method or function
    does, then you can add a few paragraphs that explain it in more depth. Don't
    be too verbose, and use an example to illustrate points. Point out any
    potential misunderstandings or problems you expect developers to have, but
    don't repeat the class documentation too much.
  -# You are obliged to then document all the parameters. Use the \c \\param
    command for that. For the description, use a short phrase such as "The 
    offset (zero based) where to begin the move." Note the capital and the dot.
  -# If the function is non-void, then you'll have to specify what it will
    return. In case of fixed values, have a look at \c \\retval. You'll use
    this one when the return type is a bool or a status_t. In case of something
    else, use \c \\return. You can also combine these two. For example, a
    method that returns a length (positive) or an error code (negative).
  -# Use \c \\see if you have any references to other methods, classes or
    global functions. At least document all the overloaded methods. Also add
    methods that do the opposite of this method, or methods that are intimately
    related.
  
  In case of overloaded members, you'll need to make a decision. If you need to
  copy too much information, you might resort to putting it in one paragraph
  with the text "This is an overloaded member function, and differs from
  \<name\> only by the type of parameter it takes." That will keep the copying
  down and will point developers right to the place where they can get more
  documentation.
  
  Again, like class descriptions, you'll have to find a good middle-ground
  between too much information, and too little. Again, write for the broadest
  audience possible, and resort to notes and warnings for specialised 
  audiences.
  
  \subsection style_variables Enumerations, Variables and Defines
  
  This section helps you document (member) variables and defines that define
  constants, as well as enumerations and their values. If you need to document
  a \c \#define macro that takes arguments, have a look at \ref style_members .
  
  The \c \\brief description of all these types follow a similar structure. 
  They are a short phrase that mention what the variable contains. Example:
  
  \verbatim
/*!
  \var char* BString::fPrivateData
  \brief BString's storage for data.

  This member is deprecated and might even become \c private in future releases.

  If you are planning to derive from this object and you want to manipulate the
  raw string data, please have a look at LockBuffer() and UnlockBuffer().
*/
  \endverbatim
  
  The variables you are going to encounter are either \c public or 
  \c protected member variables, or global variables that have a certain
  significance. In the case of member variables, you'll need to document what
  they mean and how the developer should manipulate them. If the class is one 
  that is meant to be derived from, make sure that in the description of the
  variable you mention how it interacts with the others, and how the developer
  should make sure that the internal coherence of the data and code members of
  the inherited class is maintained. 
  
  Global variables will mostly be constants. If so, document what they stand
  for and what they might be used for, as well as which classes and functions
  depend on that constant. If the variable is meant to be changed by the
  developer, explain what values are valid and which functions and classes
  depend on this variable. 
  
  Defines are usually used as message constants. Give a short description of
  what the message constant stands for, and where it might be send from and
  where it might be received.
  
  Enumerations can either be anonymous or named. In case of the latter, you can
  give a description of the enumeration in a documentation block that starts
  with an \c \\enum command, followed by the name of the enumeration. If the
  enumeration is within the scope of a class, prepend the classname and the 
  scope indicator. In case of an anonymous enum, you can only document the
  individual members (which you should do for the named enumerations as well),
  which can be done within code blocks that start with the \c \\var command.
  Doxygen will know that it's an enumeration value, don't worry about mixups.
  If the enumeration value is within a class, prepend the classname and scope
  indicator. Give a short description of the value, which methods react to it, 
  where it might be used, etcetera. Don't go as far as to copy information too 
  much. For example, if you use an enumeration in only one class and you
  document the possible values there, then don't do that again for the
  enumeration documentation: rather just refer to it. That sort of documentation
  belongs to the class description, not to the enumeration.
  
  \subsection style_groups Groups
  
  If you subdivide members of classes into groups, you have the ability to apply
  some general information that will be listed above the listing of the members
  in that group. See the section \ref commands_grouping on how to define groups.
  This section is on what to put in the header block.
  
  First of all, it's probably a good idea to give your group a name. This name
  will be printed as a title and will enhance the clarity of what the group
  contains. If you put the \c \\name command as the first command of a group,
  the rest of the words on that line will be used as the title. You should
  choose simple titles of no more than three words.
  
  It's possible to add one or two paragraphs of information. These paragraphs
  should contain some quick notes on which of the members in that group to use
  for what purpose. See it as a quick subdivision that a developer could use as
  a guide to see which method he actually wants to use. Don't go on describing
  the methods in detail though, that's what the member documentation is about.
  Have a look at the example:
  
  \verbatim
/*!
  \name Comparison Methods

  There are two different comparison methods. First of all there is the whole
  range of operators that return a boolean value, secondly there are methods
  that return an integer value, both case sensitive and case insensitive.

  There are also global comparison operators and global compare functions.
  You might need these in case you have a sort routine that takes a generic
  comparison function, such as BList::SortItems().
  See the String.h documentation file to see the specifics, as they are
  basically the same as implemented in this class.
*/
  \endverbatim
  
  Straight, to the point, gives no more information than necessary. Divides
  the members up into two groups and refers to other functions the developer
  might be looking for. The hard limit is two (short) paragraphs. Using more
  will not improve clarity.

*/