
namespace Wt {

/*!

  \mainpage %Wt documentation.

   <a href="http://www.webtoolkit.eu/wt">%Wt</a> is a C++ library for
   developing web applications.
  
   For learning web application programming with %Wt, we recommend
   reading the <a href="../../tutorial/wt.html"> hands-on introduction
   to %Wt</a>, which includes a complete tutorial (reworked in
   December 2011).

   This is a reference manual which has been generated from the source code,
   which we aim to be thorough and complete. There are a number of starting
   points we recommend for specific information:

   In addition, there is also:
   - \ref overview - Overview of the main %Wt components (recommended!).
   - \ref InstallationUnix - How to build %Wt and your applications
     on Unix-like systems.
   - \ref InstallationWindows - How to build %Wt and your applications on
     Microsoft Windows systems.
   - \ref Releasenotes - Release notes.
   - \ref ext - Using %Ext widgets, widgets based on ExtJS.
   - \ref example - A line-by-line explanation, mainly shows how to implement
      client-side event handling in C++ (a parodox!).
   - <a href="../../tutorial/dbo.html">Tutorial for Dbo</a> - %Wt's C++ ORM
     library.
   - <a href="../../tutorial/auth.html">Tutorial for Auth</a> - %Wt's
     Authentication module.
   - <a href="../../examples/html/modules.html">Examples documentation</a>.

   \page overview Library overview
  
   \section contents Contents
  
   <div style="margin-left: 10px; margin-bottom: 5px;">
   \ref wwidget_sec
     <div style="margin-left: 10px; margin-bottom: 7px;">
     \ref layout <br>
     \ref style <br>
     \ref containers <br>
     </div>
   \ref urls_sec <br>
     <div style="margin-left: 10px; margin-bottom: 7px;"></div>
   \ref application_sec <br>
     <div style="margin-left: 10px; margin-bottom: 7px;"></div>
   \ref signal_slot <br>
     <div style="margin-left: 10px; margin-bottom: 7px;"></div>
   \ref eventhandling <br>
     <div style="margin-left: 10px; margin-bottom: 7px;"></div>
   \ref bootstrap <br>
     <div style="margin-left: 10px; margin-bottom: 7px;">
     \ref default_bootstrap <br>
     \ref progressive_bootstrap <br>
     </div>
   \ref sec_painting <br>
     <div style="margin-left: 10px; margin-bottom: 7px;"></div>
   \ref internationalization_sec <br>
     <div style="margin-left: 10px; margin-bottom: 7px;"></div>
   \ref deployment <br>
     <div style="margin-left: 10px; margin-bottom: 7px;">
     \ref fastcgi <br>
     \ref wthttpd <br>
     \ref wtisapi <br>
     </div>  
   \ref configuration_sec
     <div style="margin-left: 10px; margin-bottom: 7px;">
     \ref config_session <br>
     \ref config_general <br>
     \ref config_fastcgi <br>
     \ref config_wthttpd <br>
     \ref config_isapi <br>
     </div>
     <div style="margin-left: 10px; margin-bottom: 7px;"></div>
   \ref error_sec
   </div>
  
   \section wwidget_sec &nbsp;1. Widgets
  
   The WWidget class represents a widget, which provides an
   abstraction of a visual entity. The entire user-interface is
   specified by creating a hierarchical structure of WWidgets, rooted
   at WApplication::root(). By reacting to events related to these
   widgets, you can perform business logic, and manipulate the widget
   hierarchy to update the user interface.

   When inserting a widget in the widget hierarchy, ownership is
   transferred to its parent in the tree. Thus, when deleting a
   widget, all of its children are deleted as well, significantly
   reducing the burden of memory management related to widgets. When
   the WApplication object is deleted, the root of the tree is
   deleted, and in this way all resources associated with any widget
   are free'd.
  
   Any descendent class of WWidget is a self-contained (reusable)
   class that encapsulates both the look and behaviour, enabling the
   design of the user interface in an orthogonal way.

   \subsection layout 1.1 Layout
  
   Widgets are layed out (with a few exceptions) following this
   hierarchical structure. You have two choices for lay-out of
   children within a container.

    - Either you use a CSS based layout (perhaps in combination with a
   WTemplate for the HTML markup), in which case the CSS style
   properties of the container and children together determine the
   result: each child manages its layout with respect to its sibling
   following a (rather complex) set of rules.

   - Alternatively, %Wt provides \link WLayout layout managers\endlink
   that may be used for layout, and this is especially useful for
   scenarios when CSS is not adequate

   CSS distinguishes between inline and block level elements (widgets)
   for deciding how to add them to the layout. Text-like widgets
   (\link WWidget::setInline(bool) inline\endlink) flow with sibling
   inline widgets in lines, wrapping at the right edge of the parent
   container. In contrast, widgets displayed as a \link
   WWidget::setInline(bool) block \endlink stack vertically with
   respect to sibling widgets. Block widgets allow more control over
   their position and size than inline widgets, and may also float to
   the left or right border of the parent container.

   Layout managers are implemented by classes that derive from
   WLayout, and are used in conjunction with the WContainerWidget
   container. A layout manager adapts the size and location of the
   children to the width and height of the parent. If you want the
   opposite (i.e. to adapt the size (width and/or height) of the
   parent to the size of the children, then you can still use layout
   managers, but you need to set additional alignment flags which
   determines how the layout is positioned in the parent in case of
   excess width and/or height.

   \subsection style 1.2 Style

   For visual markup of widgets, the recommended way is to use CSS
   style sheets. These allow the visual look to be defined seperately
   from the the rest of the application. External stylesheets may be
   loaded using WApplication::useStyleSheet(), and the internal
   stylesheet may be manipulated using WApplication::styleSheet().

   In the stylesheets, you describe rules that are prefixed by CSS
   selectors. By setting matching style classes for your widgets using
   WWidget::setStyleClass(), these rules will be applied to your
   widgets. The recommended way for visual response to events is by
   changing the style class for the widget.

   In addition to style sheets, %Wt also supports the direct
   manipulation of a widget's style, using WWidget::decorationStyle().

   \subsection containers 1.3 Widget containers
  
   With a few exceptions, all widgets are child of (and contained in)
   a container widget such as WContainerWidget or WTableCell. A widget
   may be inserted into a WContainerWidget by adding the widget to the
   container using WContainerWidget::addWidget(), or by passing the
   parent container as an argument to its constructor. You may also
   add a widget to a container using a layout manager.

   \section urls_sec &nbsp;2. Application URL(s)

   A %Wt application, like any other CGI application, is deployed at a
   single location (URL) within your web server. In this mode, a %Wt
   application is a single page web application: the URL does not
   change. Still, an application may manage multiple URLs that
   correspond to internal paths. These are URLs that are created by
   appending an internal path to the application URL. The internal
   path may be manipulated through WApplication::setInternalPath().
   When the internal path changes, this is reflected in the browser
   URL and an entry is added to the browser history, allowing the user
   to use the back and forward buttons to navigate through your
   application.

   To avoid rerendering the entire widget tree for each internal path
   change, when Ajax is available, the internal path is indicated
   either by manipulating the URL using the HTML5 History API, or by 
   using a name anchor (#) after the deployment URL. For a plain HTML
   session, the session ID is appended to the URL to avoid the session
   from reloading when the user navigates using a WAnchor to a new
   internal URL.

   To effectively change the internal path and obtain consistent
   behaviour with or without JavaScript, you should use a WAnchor to
   let the user navigate to a new internal path. The easiest way to do
   this is by using the WAnchor::setRefInternalPath(). This refers the
   WAnchor to a URL generated by WApplication::bookmarkUrl() for the
   new internal path (handling the plain HTML case), and binds a
   JavaScript slot to its WAnchor::clicked() signal, which changes the
   internal path (handling the Ajax case).

   Finally, you can listen for path changes using the
   WApplication::internalPathChanged() event to react to the user
   navigating through his history.

   \section application_sec &nbsp;3. Startup and session management
  
   In your application, e.g. from within your main(), you should
   WRun() to start the %Wt application server. This method will return
   only when shutdown is signaled by the environment, and after the
   application server (and all remaining active sessions) has been
   properly shut down. One parameter to the WRun() function is a \em
   createApplication function object. Alternatively, if you wish to
   have more control over the application server, you may also
   instantiate and configure a WServer instance directly.

   For every new session (which corresponds to a new user accessing
   your web application), the library calls your createApplication
   callback function to create a new WApplication object for that
   session. The request arguments (as part of the WEnvironment object)
   are passed to this createApplication function, and may be used to
   customize the application or authenticate the user. See also \ref
   bootstrap for details on the application bootstrap method.
  
   At all times, the WApplication instance is accessible using the
   static method WApplication::instance(), and is useful to inspect
   startup arguments and settings (using WApplication::environment()),
   to set or change the application title (WApplication::setTitle()),
   to specify a locale (WApplication::setLocale()) for rendering, and
   many other application-wide settings. In a multi-threaded
   environment, access to this instance is implemented using thread
   local storage.
  
   A session exits when the user browses away from the application,
   when WApplication::quit() is called, or when the application server
   is shut down. In any case, the application object together with the
   entire widget tree for that session is first properly
   deleted. Therefore, you should release resources held by your
   widgets or application in the destructors of these objects.
  
   The library offers two different mechanisms to map sessions onto
   processes: <b>dedicated processes</b> (only with FastCGI
   deployment) and <b>shared processes</b>. The first mechanisms forks
   a dedicated process for every distinct session. This provides the
   kernel-level isolation of different sessions, which may be useful
   for highly security sensitive applications. The second mechanism
   spawns a number of processes and allocates new sessions randomly to
   one of these processes (when using the built-in httpd, only one
   process is used in total). This reduces the danger for DoS attacks,
   but requires more careful programming as memory corruption affects
   all sessions in a single process, and sessions are not isolated by
   any other mechanism but correct programming.

   \section signal_slot &nbsp;4. Signal/slot event handling
  
   To respond to user-interactivity events, or in general to communicate
   events from one widget to any other, %Wt uses a signal/slot system.
  
   A slot can be any function, bound using boost::bind() or
   std::bind(), but special support exists for method of descendants
   of WObject with respect to connection management: the signal will
   be disconnected when the bound object is deleted.

   To connect a signal with a slot, the only requirement is that the
   method signature of the slot must be compatible with the signal
   definition. In this way every method may be used as a slot, and it
   is not necessary to explicitly indicate a particular method to be a
   slot (as is needed in Qt), by putting them in a special
   section. Nevertheless, you may still do that if you wish to
   emphasize that these functions can be used as slots, or, if you
   have done extra work to optimize the implementation of these
   methods as client-side JavaScript code (see below).
  
   A signal may be created by adding a \link Signal Signal<X,
   ...>\endlink object. You may specify up to 6 arguments which may be
   of arbitrary types that are Copyable, that may be passed through
   the signal to connected slots.
  
   The library defines several user-event signals on various widgets,
   and it is easy and convenient to add signals and slots to widget
   classes to communicate events and trigger callbacks.
  
   Event signals (\link EventSignal EventSignal<E>\endlink)
   are signals that may be triggered internally by the library to
   respond to user interactivity events. The abstract base classes
   WInteractWidget and WFormWidget define most of these event
   signals. To react to one of these events, the programmer connects a
   self-defined or already existing slot to such a signal.
  
   \section eventhandling &nbsp;5. Optimizing client-side event handling
  
   By default, %Wt performs all event processing server-side. Every
   connected event signal will cause the web browser to communicate
   with the web server in order to invoke the call-back code, and
   visual changes will be updated in the web page.
  
   However, %Wt offers several options for incorporating client-side event
   handling. This may in general increase responsiveness of the application
   since the user gets an instant feed-back, avoiding the typical
   communication delay is avoided.
  
   The least flexible but most convenient option for client-side event
   handling is letting %Wt learn the visual effect of a slot and cache
   it in JavaScript code in the browser.  In this way, the
   functionality is still specified in C++, and therefore the
   application still works equally when JavaScript is not available.
   The only restriction is that this is only possible for stateless
   call-back code -- i.e. when the visual update does not depend on
   state that may change in the course of the application, or event
   details.  See the documentation of WObject::implementStateless
   for details, or the \ref example for the use of stateless
   implementations to create a treelist widget that does all node
   expansion / collapsing client-side, at least if JavaScript is
   available.
  
   The stateless slot learning allows applications to be developed entirely
   in C++, with only one specification of the desired behaviour, and decide
   at run-time to optimize certain event handling in client-side JavaScript
   if possible, and fall-back to server-side event handling otherwise.
  
   When the requirements for stateless slot learning cannot be met you will
   have to resort to writing JavaScript manually. %Wt provides a number
   of mechanisms to integrate JavaScript code with C++:

   - Using JSlot, you can specify the JavaScript for a slot, when
     connected to an EventSignal.

   - Using JSignal, you can emit a C++ signal from JavaScript code,
     using a JavaScript function <tt>Wt.emit()</tt>.

   - Using WApplication::doJavaScript(), you can call JavaScript code
     directly as part of event handling.

  \section bootstrap &nbsp;6. Application bootstrap

  A %Wt application may support both plain HTML and Ajax-enabled user
  agents. When a first request is made for a new session, there is no
  way of knowing whether the agent supports Ajax (and has it
  enabled). The bootstrap procedure therefore has two strategies of
  making the choice between a plain HTML and Ajax-enabled application
  mode.

  \subsection default_bootstrap 6.1 Default bootstrap

  In the default bootstrap mode, for the normal case, a small
  bootstrap HTML file is served, which detects presence of Ajax (and
  various other environment properties such as presence of an internal
  path as an anchor, cookie support, and IE VML DPI setting). If no
  JavaScript support is available, it automatically redirects the user
  to a plain HTML version of the application.

  In this mode, the application is not started until the library has
  determined Ajax support, which is made available in
  WEnvironment::ajax() which is passed to the application constructor.

  In some special cases, this bootstrap is skipped and a plain HTML
  version is served. This is for user agents that are identified as
  spider bots, or user agents which are configured to not support Ajax
  (well), see the \ref config_general "user-agents configuration setting".

  There are some draw-backs to this bootstrap method:

  - the redirection without JavaScript support may not be supported by
    all user agents, leaving these with a link and a redirect message
    (see the \ref config_general "redirect-message configuration
    setting")

  - there is an additional round-trip before any contents is rendered
 
  - for an Ajax user interface, all contents will be loaded through
    JavaScript. This has a draw-back that some 3rd party JavaScript
    libraries do not support being loaded on-demand (with as most
    notable example, Google ads).

  \subsection progressive_bootstrap 6.1 Progressive bootstrap

  Since %Wt 2.99.4, a new bootstrap method has been added (initially
  proposed by Anthony roger Buck). While the default bootstrap already
  honors the principle of graceful degradation, this bootstrap
  implements this using the principle of <a
  href="http://en.wikipedia.org/wiki/Progressive_enhancement">progressive
  enhancement</a> (and quite literally so).

  This bootstrap method may be enabled with the \ref config_general
  "progressive-bootstrap configuration setting".

  This bootstrap method will initially assume that the user agent is a
  plain HTML user-agent and immediately create the application (with
  WEnvironment::ajax() always returning <tt>false</tt>). The initial
  response will contain the initial page suitable for a plain HTML
  user-agent.

  JavaScript embedded in this page will sense for Ajax support and
  trigger a second request which progresses the application to an Ajax
  application (without repainting the user interface). To that extent,
  it will change WEnvironment::ajax() to return <tt>true</tt>, and
  invoke WApplication::enableAjax() which in turn propagates
  WWidget::enableAjax() through the widget hierarchy. This upgrade
  happens in the back-ground, unnoticed to the user.

  This mitigates disadvantages associated with the default bootstrap,
  but has the drawback of requiring consistent enableAjax() implementations
  and requiring more server-side processing.

  \section sec_painting &nbsp;7. Painting

  %Wt provides a vector graphics painting system which depending on
  the browser support uses one of three different methods to paint the
  graphics (inline SVG, inline VML or HTML 5 &lt;canvas&gt;
  element). Vector graphics has as benefit a lower bandwidth usage,
  which is indepedent of the image size and quality, and can be
  embedded within the HTML, avoiding an additional round-trip. To use
  the paint system, you need to specialize WPaintedWidget and use a
  WPainter to paint the contents of the widget inside its
  WPaintedWidget::paintEvent().

  \section internationalization_sec &nbsp;8. Internationalization

  %Wt's WString class offers an interface to translate strings by
  using the static WString::tr("key") method to construct a WString.
  These key values will be lookup up in so-called message resource
  bundles (see WMessageResourceBundle). These are a set of xml files
  that translate the keys to a localized string. The name of the xml
  file determines the language contained therein (e.g. foo.xml, foo-nl.xml,
  foo-cn.xml)

  The strings that are used by classes within the %Wt library use the
  same system to translate their strings. English messages will be
  used by default and are built into %Wt. If you want to translate e.g.
  the months of a WCalendar, copy src/xml/wt.xml and translate them to
  your language of choice. From then on, you can call
  WMessageResourceBundle::use() in your application and use your own
  replacement XML files, which will take precedence over the built-in
  translations.

  %Wt also supports plural forms of nouns, to translate such string
  use the static WString::trn("key", n) function. The WMessageResourceBundle
  class documentation contains an example on how to format the xml resource 
  bundle to use this functionality. 

  \section deployment &nbsp;9. Deployment

  The library is designed so that, besides the application binary,
  only files from the <tt>resources/</tt> folder are needed to deploy
  the application. The resources folder contains icons, style sheets
  associated with themes, and other resources specific for special
  widgets. The URL at which the <tt>resources/</tt> folder is deployed
  is based on the <i>resourcesURL</i> configuration property (see see
  \ref config_general "configuration properties"), which defaults to
  "/resources".

  In addition, you may need to deploy also your own CSS files, custom
  icons/images, and/or static pages that you reference from your
  application, into your web server.

  Your application may also use other files which do not need to be
  published online, but are instead read only by your
  application. These files include message resource files (containing
  localized text strings), the wt configuration file, your own
  configuration files, etc... You can deploy these to an
  <i>application root</i> (see WApplication::appRoot()), whose
  location is configured in a way that is specific for each connector.

  \subsection fastcgi 9.1 FastCGI

  When linking your application against <tt>libwtfcgi</tt>, the
  resulting binary is a FastCGI binary. This binary may then be
  deployed and managed within a web server which supports the FastCGI
  protocol (these include apache, lighttpd and many other popular web
  servers).

  The following locations for the wt_config.xml configuration file are
  considered, in this order:

  - value of environment variable <tt>$WT_CONFIG_XML</tt>
  - within the app root, as configured by the environment variable
    <tt>$WT_APP_ROOT</tt>: <tt>$WT_APP_ROOT/wt_config.xml</tt>
  - the compile-time default (<tt>/etc/wt/wt_config.xml</tt>),

  Environment variables can be specified to a FastCGI application depending
  on the web server. E.g. for FastCGI, this is:

\code
-initial-env WT_APP_ROOT=/opt/myapp
\endcode

  \subsection wthttpd 9.2 Built-in httpd

  When linking your application against <tt>libwthttp</tt>, the
  resulting binary is a stand-alone HTTP/WebSockets server.  The web
  server will act as a plain web server in addition to serving the %Wt
  application.

  The following locations for the wt_config.xml configuration file are
  considered, in this order:

  - command-line parameter <tt>--config</tt> or <tt>-c</tt>
  - value of environment variable <tt>$WT_CONFIG_XML</tt>
  - within the appRoot, as configured by command line paramater
    <tt>--approot</tt>, or the environment variable <tt>$WT_APP_ROOT</tt>:
    appRoot<tt>/wt_config.xml</tt>
  - the compile-time default (<tt>/etc/wt/wt_config.xml</tt>)

  Use the <tt>--deploy-path</tt> parameter to deploy the application at
  a specific URL. By default, the application is deployed at '/'.

  When the application is deployed at a path ending with '/' (i.e. a
  folder path), only an exact match for a requested URL will be routed
  to the application itself. This behaviour avoids deployment problems with
  the singular case where you deploy at '/' and no static files would
  be served by the web server. As a consequence, ugly URLs will be
  generated for internal paths. Since version 3.1.9, it is however
  possible to have clean URLs also when deploying at the root by
  specifically listing the folders that contain static assets in
  --docroot, followed by ';':

  \code
$ ../../build/examples/wt-homepage/Home.wt --docroot=".;/favicon.ico,/css,/resources,/style,/icons" ...
  \endcode

  \subsection wtisapi 9.3 ISAPI

  When linking your application against <tt>wtisapi</tt>, the
  resulting binary is an ISAPI plugin. This DLL may then be
  deployed and managed within Microsoft IIS.

  The following locations for the wt_config.xml configuration file are
  considered, in this order:

  - within the app root, as configured by the INI file which has the same
    name as the application DLL, but with .INI append to it
    (e.g. \htmlonly <tt>C:\Program Files\WtApplications\Public\MyApplication.dll.ini</tt> \endhtmlonly):
\htmlonly <pre>
[isapi]
appRoot=C:\Program Files\MyApplications\AppRoot
</pre> \endhtmlonly
  - the compile-time default (<tt>/etc/wt/wt_config.xml</tt>)
 
  \section configuration_sec &nbsp;10. Configuration

  %Wt has one main XML configuration file, which by default is located
  in <tt>/etc/wt/wt_config.xml</tt>, but whose location can be overridden
  use environment settings and/or commandline parameters that are connector
  specific (see the connector supra).

  The configuration file may specify several
  <b>&lt;application-settings&gt;</b>. The settings that apply are
  determined by the <i>location</i> attribute. Application settings
  for the '*' location are general settings, which may be overridden
  on a per-application level by settings with a location attribute
  that matches the location of the application (on the file system).

  \subsection config_session 10.1 Session management (wt_config.xml)

  These are options related to session management, and are specified
  inside <b>&lt;session-management&gt;</b> subsection.

  <dl>

    <dt><strong>dedicated-process</strong></dt>

    <dd>Every session is mapped a dedicated process, allowing maximal
      session isolation, but at an increased session cost. <br>
      This is currently only supported using the FastCGI connector.</dd>

    <dt><strong>shared-process</strong></dt>

    <dd>Sessions share a fixed number of processes, yielding a lower
      session cost. <br>
      This is the only option for the Wthttpd connector.</dd>

    <dt><strong>tracking</strong></dt>

    <dd>How session tracking is implemented: automatically (using
      cookies when available, otherwise using URL rewriting) or
      strictly using URL rewriting (which allows multiple concurrent
      sessions from one user).  </dd>

    <dt><strong>reload-is-new-session</strong></dt>

    <dd>Should a brower reload spawn a new session (convenient for
      debugging) or simply refresh (using WApplication::refresh()) the
      current session ? This setting may have implications for the URL
      that is displayed, because session information in needed in the
      URL to handle the reload within the current session.</dd>

    <dt><strong>timeout</strong></dt>

    <dd>The timeout (in seconds) for detecting an idle session. A %Wt
      application uses a keep-alive messages to keep the session alive
      as long as the user is visiting the page. Increasing this number
      will result in a longer time between keep-alive message,
      resulting in a lower server load, but at the same time will
      detect a dead session with a longer delay, and thus have on
      average more sessions in memory that are no longer used.</dd>
  
    <dt><strong>server-push-timeout</strong></dt>

    <dd>When using server-initiated updates, the client uses
      long-polling requests or WebSockets. Proxies (including reverse
      proxies) are notorious for silently closing idle requests; the
      client therefore cancels the long polling request after a
      timeout, and starts a new one, or does a ping/pong message over
      the WebSocket connection.</dd>

  </dl>

  \subsection config_general 10.2 General application settings (wt_config.xml)

  These options are indicated directly within
  <b>&lt;application-settings&gt;</b>, and specify settings that
  affect the run-time behaviour of the application.

  <dl>
    <dt><strong>debug</strong></dt>

    <dd>When debugging is enabled, JavaScript errors are not caught,
    and thus will provide stack information when using a JavaScript
    debugger.</dd>

    <dt><strong>log-file</strong></dt>

    <dd>Path to the log file used for application logging (see
      Wt::log()). If not specified, logging is directed to stderr,
      which depending on the connector used ends up in the server
      error log, into the big void, or, simply to stderr.  </dd>

    <dt><strong>log-config</strong></dt>

    <dd>Configuration for the built-in logger, which is passed on to
    WLogger::configure()</dd>

    <dt><strong>max-request-size</strong></dt>

    <dd>The maximum HTTP request size (Kb) that is accepted. An oversized
      request will result in a WApplication::requestTooLarge() signal.
      </dd>

    <dt><strong>session-id-length</strong></dt>

    <dd>The length (in number of characters) for the unique session ID.</dd>

    <dt><strong>session-id-prefix</strong></dt>

    <dd>A fixed prefix for the session ID. You can use this to implement
      aid a load-balancer to figure out the destination for a particular
      request.</dd>

    <dt><strong>plain-ajax-sessions-ratio-limit</strong></dt>

    <dd>DoS prevention: limit plain HTML sessions. This is a simple
      measure which avoids Denial-of-Service attacks on plain HTML
      sessions, which are easy to mount in particular in the case of
      progressive bootstrap mode. This setting may be used to keep the
      ratio of plain HTML versus Ajax sessions under a certain
      ratio. Typically, most of your sessions will be Ajax sessions,
      and only a tiny fraction (e.g. less than 5%) will be plain HTML
      sessions. This ratio is only enforced when more than 20 sessions
      have been created.  </dd>

    <dt><strong>ajax-puzzle</strong></dt>

    <dd>DoS prevention: adds a puzzle to validate Ajax sessions.  This
      is a simple measure which avoids Denial-of-Service attacks on
      Ajax sessions. When enabled, a puzzle needs to be solved in the
      first Ajax request which eliminates agents that do not build a
      proper DOM tree.  </dd>

    <dt><strong>send-xhtml-mime-type</strong></dt>

    <dd>Whether the application presents rendered content as XHTML or
      HTML. %Wt always renders XHTML1 compatible HTML, but by default
      indicates to the browser that it is in fact HTML. Before the adoption
      of HTML5, use inline SVG (see WSvgImage), it was necessary to present
      an XHTML mime type. Setting this option will do so only for
      browsers that indicate support for XHTML. Nowadays, this option
      is rarely useful.</dd>

    <dt><strong>web-sockets</strong></dt>

    <dd>By default Ajax and long polling are used to communicate
      between server and browser.

      By enabling web socket support, if the browser supports
      WebSockets, then WebSocket is the protocol used for
      communication between client and server. WebSockets are
      currently only supported by the built-in httpd Connector, which
      acts as both an HTTP and WebSocket server, multiplexed on the
      same port(s).

      %Wt implements the final Web Sockets RFC candidate, as well as
      all prior drafts.</dd>

    <dt><strong>redirect-message</strong></dt>

    <dd>When the default bootstrap method is used, this message is used
    in the link which redirects to the user to a plain HTML version, in
    case his user agent does not support the automatic redirect.</dd>

    <dt><strong>behind-reverse-proxy</strong></dt>

    <dd>When enabling this option to indicate that the application is
      deployed behind a reverse proxy (as would be common if you use
      the wthttpd connector), the server location is not read from the
      "Host" header, but from the <tt>X-Forwarded-For</tt> header, if
      present.</dd>

    <dt><strong>user-agents</strong></dt>

    <dd>%Wt considers three types of sessions:
      <ul>
        <li>Ajax sessions: use Ajax and JavaScript</li>
	<li>plain HTML sessions: use plain old server POSTs</li>
	<li>bots: have clean internal paths, no persistent sessions, no
	  html &lt;form&gt; elements, and no auto-generated DOM element
	  id's.</li>
      </ul>

      <p>By default, %Wt does a browser detection to distinguish
      between the first two: if a browser supports JavaScript (and has
      it enabled), and has an Ajax DOM API, then Ajax sessions are
      chosen, otherwise plain HTML sessions.</p>

      <p>Here, you may indicate which user agents should or should
      not receive an Ajax session regardless of what they report as
      capabilities, and which user agents should be treated as search bots.
      You can define three types of <user-agents> lists:

      - <tt>type="ajax" mode="white-list"</tt>: these are the only
      user agents that are considered as Ajax-capable.
      - <tt>type="ajax" mode="black-list"</tt>: these are user agents that
      are not considered as Ajax-capable.
      - <tt>type="bot"</tt>: these are user-agents that are treated as bots.
      </p>

      Example:

      \code
<user-agents type="bot">
  <user-agent>.*Googlebot.*</user-agent>
  <user-agent>.*msnbot.*</user-agent>
  <user-agent>.*Slurp.*</user-agent>
  <user-agent>.*Crawler.*</user-agent>
  <user-agent>.*Bot.*</user-agent>
  <user-agent>.*ia_archiver.*</user-agent>
  <user-agent>.*Twiceler.*</user-agent>
  <user-agent>Yandex.*</user-agent>
  <user-agent>.*Nutch.*</user-agent>
  <user-agent>.*MJ12bot.*</user-agent>
  <user-agent>Baiduspider.*</user-agent>
</user-agents>
      \endcode

    </dd>

    <dt><strong>progressive-bootstrap</strong></dt>

    <dd>This boolean configuration option configures which bootstrap
      method is used, see \ref bootstrap.
    </dd>

    <dt><strong>properties</strong></dt>

    <dd>Application-specific properties which may be accessed using
      WApplication::readConfigurationProperty(). For example:
      \code
 <properties>
    <property name="extBaseURL">/ext/</property>
    <property name="resourcesURL">/resources</property>
    <property name="appRoot">/opt/myapp</property>
 </properties>
      \endcode
    </dd>
  </dl>

  \subsection config_fastcgi 10.3 FastCGI options (wt_config.xml)

  These options only apply to FastCGI-based deployment, and are
  are specified inside a <b>&lt;connector-fcgi&gt;</b> subsection.

  <dl>
    <dt><strong>valgrind-path</strong></dt>

    <dd>Set the path to valgrind for debugging using valgrind. This
    requires that debugging is enabled and <tt>debug</tt> is passed to
    the application as last request parameter.</dd>

    <dt><strong>run-directory</strong></dt>

    <dd>The path that is used by the library for managing sessions.</dd>
  </dl>

  \subsection config_wthttpd 10.4 Wt httpd (command-line or configuration file) options

These options are not specified in the wt_config.xml configuration
file, but may be indicated on the command-line, or within a
configuration file that is located at /etc/wt/wthttpd.

The configuration file syntax is line based:
<ul>
      	<li>
		<p>A line in the form:</p>
		<p><code>name = value</code></p>
		<p>gives a value to an option.</p>
	</li>

	<li>
		<p>The <code>#</code> character introduces a
        	comment that spans until the end of the line.</p>
	</li>
</ul>

\code
Allowed options:

General options:
  -h [ --help ]                 produce help message
  -t [ --threads ] arg (=10)    number of threads
  --servername arg (=vierwerf)  servername (IP address or DNS name)
  --docroot arg                 document root for static files, optionally 
                                followed by a comma-separated list of paths 
                                with static files (even if they are within a 
                                deployment path), after a ';' 
                                
                                e.g. --docroot=".;/favicon.ico,/resources,/style"

   --approot arg                application root for private support files; if 
                                unspecified, the value of the environment 
                                variable $WT_APP_ROOT is used, or else the 
                                current working directory
  --docroot-static arg          comma-separated list of paths that correspond 
                                to static files, even if they are within a 
                                deployment path
  --errroot arg                 root for error pages
  --accesslog arg               access log file (defaults to stdout)
  --no-compression              do not use compression
  --deploy-path arg (=/)        location for deployment
  --session-id-prefix arg       prefix for session-id's (overrides 
                                wt_config.xml setting)
  -p [ --pid-file ] arg         path to pid file (optional)
  -c [ --config ] arg           location of wt_config.xml; if unspecified, the 
                                value of the environment variable 
                                $WT_CONFIG_XML is used, or else the built-in 
                                default (/etc/wt/wt_config.xml) is tried, or 
                                else built-in defaults are used
  --max-memory-request-size arg threshold for request size (bytes), for 
                                spooling the entire request to disk to avoid, 
                                to avoid DoS
  --gdb                         do not shutdown when receiving Ctrl-C (and let 
                                gdb break instead)

HTTP/WebSocket server options:
  --http-address arg    IPv4 (e.g. 0.0.0.0) or IPv6 Address (e.g. 0::0)
  --http-port arg (=80) HTTP port (e.g. 80)

HTTPS/Secure WebSocket server options:
  --https-address arg     IPv4 (e.g. 0.0.0.0) or IPv6 Address (e.g. 0::0)
  --https-port arg (=443) HTTPS port (e.g. 443)
  --ssl-certificate arg   SSL server certificate chain file
                          e.g. "/etc/ssl/certs/vsign1.pem"
  --ssl-private-key arg   SSL server private key file
                          e.g. "/etc/ssl/private/company.pem"
  --ssl-tmp-dh arg        File for temporary Diffie-Hellman parameters
                          e.g. "/etc/ssl/dh512.pem"

Settings may be set in the configuration file /etc/wt/wthttpd
\endcode

  \subsection config_isapi 10.5 ISAPI options (wt_config.xml)

  These options only apply to ISAPI-based deployment, and are
  are specified inside a <b>&lt;connector-isapi&gt;</b> subsection.

  <dl>
    <dt><strong>num-threads</strong></dt>

    <dd>Sets the number of threads to be used to handle %Wt traffic. The
    connector will never use IIS threads to do any processing, but will
    forward the requests to a thread pool of the size given in this variable.
    Depending on your application, you may want to increase the default size
    of 10 threads.</dd>

    <dt><strong>max-memory-request-size</strong></dt>

    <dd>Every HTTP request whose size is smaller than this parameter will
    be buffered in memory. Larger requests, such as large file uploads, will
    be spooled to a file. You probably do not want to change this parameter.
    </dd>
  </dl>


   \section error_sec &nbsp;11. Error-handling and logging

   %Wt provides logging of events to a log-file (see the \ref
   config_general "log-file configuration setting"). Every log entry
   has a timestamp, the process id and the session id. %Wt uses four
   different event types, from least to most severe:

  <dl>
    <dt><strong>notice</strong></dt>

    <dd>Informational notices. These are events that may be
    interesting for late analysis of other problems, for performance
    analysis, or estimating server load.</dd>

      <p>Generated using Wt::log(), e.g.:
      \code
Wt::log("info") << "Message";
      \endcode
      </p>

    <dt><strong>warn</strong></dt>

    <dd>Warnings. These events are generated when you are using the
    API in a way that may not have been as intended.</dd>

      <p>Generated using Wt::log(), e.g.:
      \code
Wt::log("warn") << "Message";
      \endcode
      </p>

    <dt><strong>error</strong></dt>

    <dd>Non-fatal application errors. These errors indicate for
      example unexpected input from the web browser or application
      user, XML parsing problems, but not necessarily a programming
      error.

      <p>Generated using Wt::log(), e.g.:
      \code
Wt::log("error") << "Message";
      \endcode
      </p>
    </dd>

    <dt><strong>secure</strong></dt>

    <dd>Non-fatal security errors and/or notices.</dd>

    <dt><strong>fatal</strong></dt>

    <dd>Fatal application errors. These errors terminate the current
      session (but not the application server), and are errors that
      indicate a programming error. For example, this error is
      triggered by misuses of the API.

      <p>Generated by throwing a std::exception.</p>
    </dd>
   </dl>

   You can now proceed to \ref InstallationUnix or \ref InstallationWindows
*/

/*! \page example Treelist example
  
   In this example we will step through the code of the <a
   href="http://wipkip.irule.be/wt/examples/treelist/demotreelist.wt">
   Tree List example</a>. The source code of the entire example is
   available as leafs of the tree. Note that %Wt offers a Tree List
   widget as part of the library (see WTreeNode), of which this
   example is a down-stripped version.
  
   The example in particular demonstrates the use of stateless slot
   learning to simultaneously implement client-side and server-side
   event handling in C++.
  
   The tree constructed as hierarchy of tree nodes. A single tree node
   is implemented in the class TreeNode. TreeNode uses the helper
   class IconPair for rendering icons that have a state (such as the
   expand/collapse icons). We start with a walk-over of this class.
  
   \section stateicon_sec IconPair: a pair of icons that reflects state.
  
   For the implementation of the tree list expand/collapse icons, as
   well as the label icons (such as the folder icon), we use class
   IconPair. It takes a pair of icons and shows only one at a
   time. Passing clickIsSwitch = true to the constructor will make the
   icon react to click events to switch the current icon.
  
   This is the class definition of IconPair:
  
   \dontinclude examples/treelist/IconPair.h
   \skip IconPair
   \until };
  
   IconPair is a composite widget, implemented as a WContainerWidget
   which contains two WImage objects. The class defines two slots:
   IconPair::showIcon1() and IconPair::showIcon2(), which show the
   respective icon, while hiding the other icon.

   Although %Wt is a C++ (server-side) library, it can also generate
   client-side JavaScript code for instant visual response. This
   example will use this capability to implement all of the tree
   navigation at the client-side for those clients that support
   JavaScript -- as if it were implemented as a JavaScript
   library. But since everything is still plain C++ code, it works
   whatever technology is available or lacking at the client
   side. Think of a stateless slot implementation as creating a forked
   implementation, with JavaScript in the client for visual response
   -- when JavaScript is available, and C++ at the server. When no
   JavaScript is available, everything happens at the server.
  
   The key concept behind %Wt's capability to implement things at the
   client-side is stateless slot implementations. A stateless slot is,
   besides a normal C++ function that may be connected to a signal, a
   C++ function that promises to always have the same behaviour (until
   it is reset, as we will see later).
  
   This applies to the two functions showIcon1() and showIcon2(), as
   they simply set the corresponding icon, irrespective of any
   application state. The library offers two methods for stateless
   slot implementations: AutoLearned and PreLearned. An AutoLearned
   stateless slot will only "become client-side" after the first
   invocation. Applied to our tree widget, this would mean that the
   first click on any icon would require a round-trip to the server
   the first time only. An AutoLearned stateless slot simply requires
   an indication that the particular slot confirms to the contract of
   being stateless. A PreLearned stateless slot, on the other hand, is
   "client-side" from the first invocation. To implement a PreLearned
   stateless however, we need to do some extra work by providing
   methods that exactly undo the effect of the slot. We provide here
   two such undo methods: undoShowIcon1() and undoShowIcon2().
  
   Enough talk! Let's look at the implementation, starting with
   the constructor.
  
   \dontinclude examples/treelist/IconPair.C
   \skip IconPair::
   \until {
  
   IconPair inherits from WCompositeWidget. A composite widget is
   a widget which is composed from other widgets, in a way not exposed
   in its API. In this way, you may later change the implementation
   without any problem.
  
   Notice how we constructed three widgets that are used in the
   implementation: two images (icon1_ and icon2_), and a container
   (impl_) to hold them. The images are added to the container by
   passing the container as the last argument in their constructor.
  
   WCompositeWidget requires to set the implementation widget,
   which is in our case a WContainerWidget:
  
   \line setImplementation
  
   We declare the slots showIcon1() and showIcon2() as stateless
   slots, allowing for client-side optimisation, and offer an undo
   function which facilitates a PreLearned client-side implementation.
  
   The calls to WObject::implementStateless() state that the slots
   showIcon1() and showIcon2() are stateless slots, and their visual
   effect may be learned in advance. The effect of these statements is
   merely an optimization. Any non-visual effects of these slots are
   still propagated and executed, as expected.
  
   \until undoShowIcon2
  
   Next, we declare the widget to be an inline widget. An inline
   widget will be layed out following the natural flow of text (left
   to right).  This does not really matter for our example, since
   TreeNode will do the layout with a WTable, but we do so to
   provide consistency with a WImage which is also inline by
   default.
  
   \line setInline 
  
   The initial state is to show the first icon:
  
   \line hide
  
   To react to click events, we connect signals with slots:
  
   \until ; //
  
   We change the cursor to a pointer to hint that clicking these icons
   may do something useful.
  
   \until } //
  
   We also change the cursor to a pointer to
   hint that clicking these icons will in fact perform an action.
  
   The rest of the class definition is:
  
   \until } //
  
   Note the implementations of undoShowIcon1() and undoShowIcon2():
   they simply, but accurately, reset the state to what it was before
   the respective showIcon1() and showIcon2() calls.
  
   \section treenode_sec TreeNode: an expandable tree node.
  
   TreeNode contains the implementation of the tree, as a hierarchy of
   tree nodes. The layout of a single node is done using a 2x2 WTable:
  
   \verbatim
   |-----------------------|
   | +/- | label           |
   |------------------------
   |     | child1          |
   |     | child2          |
   |     | child3          |
   |     |       ...       |
   |-----------------------| \endverbatim
  
   The TreeNode manages a list of child nodes in a WContainerWidget
   which will be hidden and shown when the node is expanded or
   collapsed, and children are collapsed when the node is expanded.
  
   This is the TreeNode class definition:
  
   \dontinclude examples/treelist/TreeNode.h
   \skip class TreeNode
   \until }; //
  
   The public interface of the TreeNode provides methods to manage
   its children, and two public slots to expand or collapse the node.
   Remember, a slot is nothing more than a method (and the public slots:
   does not actually mean anything, except providing a hint to the user
   of this class that these methods are made to be connected to signals).
  
   We start with the implementation of the constructor:
  
   \dontinclude examples/treelist/TreeNode.C
   \skip TreeNode::TreeNode
   \until {
  
   We start with declaring stateless implementations for the slots.
   It is good practice to do this first, since it must be done before
   any connections are made to the slots.
  
   \until undoCollapse
  
   We will implement the treenode as 2 by 2 table.
  
   \skipline setImplementation
  
   We create all icons. Since currently the node is empty, we only
   show the no-expand version (which is simply a horizontal line).
  
   \until noExpandIcon
  
   The expanded content is a WContainerWidget.
  
   \until hide
  
   We create the label and child count text widgets:
  
   \until treenodechildcount
  
   Now we add all widgets in the proper table cell, and set the correct
   alignment.
  
   \until setContentAlignment(Wt::AlignMiddle)
  
   Finally, we connect the click events of the expandIcon to the expand
   and collapse slots.
  
   \until } //
  
   WTable::elementAt(int row, int column) is used repeatedly to add or
   modify contents of the table cells, expanding the table geometry as
   needed. Finally, we make connections from the expand and collapse
   icons to the slots we define in the TreeNode class.
  
   Again, we optimize the visual effect of expand() and collaps() in
   client-side JavaScript, which is possible since they both have an
   effect independent of application state. Typically, one will start
   with a default dynamic slot implementation, and indicate stateless
   implementations where desired and possible, using one of the two
   mechanisms of stateless slot learning.
  
   The "business logic" of the TreeNode is simply to manage its children.
   Whenever a child is added or removed, adjustments to its look are
   updated by calling childNodesChanged().
  
   \until } //
  
   The expand icon of the last child is rendered differently, as it
   needs to terminate the vertical guide line. To keep the
   implementation simple, we simply let every child reset its proper
   look by calling adjustExpandIcon().
  
   \until adjustExpandIcon
  
   When getting a first child, or losing the last child, the expand icon
   changes too.
  
   \until adjustExpandIcon
  
   We also update the childCount label.
  
   \until setText("")
  
   Finally, we call WObject::resetLearnedSlots(). Because the expand()
   slot depends on the number of children, because it needs to
   collapse all children -- this slot is not entirely stateless,
   breaking the contract for a stateless slot. However, we can get
   away with still implementing as a stateless slot, by indicating
   when the state has changed.
  
   \until } //
  
   The implementation of the collapse slot is as follows:
  
   \until {
  
   First we record the current state, so the undo method can exactly undo
   what happened.
  
   \until isHidden()
  
   Next, we implement the actual collapse logic:
  
   \until } //
  
   Similarly, the implementation of the expand slot. However, in this
   case we need to collapse all children as well.
  
   \until } //
  
   Since we implement these slots as prelearned stateless slots, we
   also need to define the undo functions. Note that Because expand()
   also collapses all child nodes, the undo function of expand() is
   not simply collapse() and vice-versa.
  
   \until } //
  
   Finally, the adjustExpandIcon() function sets the correct images,
   which depends on how the node relates to its siblings. The last
   node looks a bit different.
  
   \until {
  
   We set the expand icon images:
  
   \until (imageLine
  
   Then, we set the vertical guide line if not the last child, and nothing
   if the last child:
  
   \until } //
  
   Finally, we select the correct icon, depending on whether the node
   has children:
  
   \until } //
  
   And that's it. By using the TreeNode class in a hierarchy, we can
   create a tree widget. The tree widget will be implemented entirely
   in JavaScript, if available, and otherwise as plain HTML. In any case,
   client-side and server-side state are completely synchronized, and
   identical by definition since they are derived from the same C++ code.
  
*/
/*! \page InstallationUnix Installation: Unix-like platforms
  
   \htmlinclude INSTALL.html
*/
/*! \page InstallationWindows Installation: Windows
  
   \htmlinclude INSTALL.win32.html
*/

/*! \page Releasenotes Release notes
  
   \htmlinclude ReleaseNotes.html
 */

}
