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A **plugin** is some PHP code that:
* lives in ##phpwiki/lib/plugin/<pluginname>.php##
* implements the ~WikiPlugin interface by extending that class.

There are many plugins already distributed with ~PhpWiki. Simply look
in the ##lib/plugin## directory or see the [[PluginManager]] list or see all the
[[phpwiki:TitleSearch?s=Help/*Plugin|Help/*Plugin pages]].

To write your own, look at the [[Help:HelloWorldPlugin]] (~HelloWorld.php
in that directory), which is a minimal example of a plugin.

A ~WikiPlugin allows one to easily add new types of dynamic
content (as well as other functionality) to wiki pages within ~PhpWiki.
In this very wiki all actions which are not entirely lowercased
are implemented using plugins, and some lowercased convenience
actions also (rename, revert, setacl, diff, ...)

Note that you can NOT extend the markup syntax with a plugin, as in other wiki engines.

== Example ==

Currently, one invokes a plugin by putting something like:

{{{
<<AllPages limit=20 cols=3>>
}}}

into a regular wiki-page.  That particular example produces a list
of the first 20 existing pages in 3 columns, via the [[Help:PageList|PageList]] library.

<<AllPages limit=20 cols=3>>

== Details ==

Plugins can take certain named arguments, most do.  The values of
these arguments can be determined four different ways.  In order of precedence:

# The plugin invocation can specify the value for an argument, like so:
  {{{
  <<BackLinks page=OtherPage>>
  }}}

# The argument can be specified via an HTTP query argument.  This
  doesn't happen (is not allowed) unless the argument is mentioned in
  the plugin invocation:

  {{{
  <<BackLinks page>>
  }}}

# Default values specified in the plugin invocation:

  {{{
  <<BackLinks page||=OtherPage>>
  }}}

# The plugin must supply default values for each argument it uses.
  Such default args may be overriden by URL arguments like so:
  {{{
    BackLinks?page=ThisPage&sortby=-mtime
  }}}
  (The ~BackLinks plugin uses the current page as the default value for
  the **page** argument.)

  Most plugins using the [[Help:PageList|PageList]] library inherit their
  default arguments from the ~PageList.

=== Standard Arguments ===

Most plugins display a list of pages, via the [[Help:PageList|PageList]]
library. ~PageList provides automatic support for those arguments.

  info, exclude, author, owner, creator, sortby, limit, paging, cols, azhead,
  comma, commasep, ordered

For details see the [[Help:PageList|PageList]] library documentation.

**exclude** and **pages** accept a list of pages. Either as comma-separated list,
supporting glob-style wildcards, or via the ##<!plugin-list pluginname ~[args~] !>##
invocation syntax, where pluginname might be any plugin returning a [[Help:PageList|PageList]].

Since most plugins return a ~PageList, this ~PageList is also a common
input parameter for other plugins, actions or formats.

=== Basic Plugin Types ===

All these plugins derive from the ##~WikiPlugin## class extending the
run method,
which returns a object tree of HTML objects, and may react on any
provided arguments from the ~WikiPage (see the args below) or
optionally overridden by arguments from the url (GET or POST args),
if defined via '||='.

A basic plugin just needs the run() method, and optionally getName,
getDescription, getDefaultArguments. See the
[[Help:HelloWorldPlugin]] for a short introduction.

  **plugin** reacts on its arguments and the request and displays
  arbitrary HTML.

  **plugin-form** is used to display a input type=text box for the
  default argument **s**.

  **plugin-list** is used as argument to provide a dynamic list of
  pagenames.

  {{{
    <?plugin PluginName [args...] ?>
  }}}

  {{{
    <?plugin-form PluginName [args...] ?>
  }}}

  {{{
    <?plugin PluginName args=<!plugin-list pluginname [args...] !> ?>
  }}}

==== The box Method ====

Themes based on the "sidebar" theme may use the box method of any
plugin, which displays a **title**
and a condensed **content** in a box.

==== ~WikiPluginCached ====

Plugins deriving from the class ~WikiPluginCached must also define
the methods getPluginType(),
optionally getExpire(), managesValidators(), and dependent of the
getPluginType the methods to display the **possibly cached** result.

  getImage(), getMap() or getHtml(),

optionally also

  getAlt(), getImageType(), embedMap(), embedImg(), embedObject()

See the config.ini PLUGIN_CACHED_* settings and ~WikiPluginCached

=== Action Pages ===

The term **[[Help:ActionPage|ActionPage]]** refers to a page containing a plugin
invocation with the same or translated pluginname as the pagename.
An **action** is together with the **pagename** argument the basic
~PhpWiki argument.
It can both be GET or POST actions. Actions are untranslated, always
English, pagenames can be localized.
Basic (and old) actions are all lowercase, like edit, browse, remove, ...
Newer actions in ~CamelCase are invoked via plugins on their
specific action page.

We decoupled actions from plugins via action pages for the following
reasons:

# Support translated action buttons and customizable action descriptions.
# Customize standard actions by tuning the plugin invocation arguments.
  Override or add plugin defaults.
# Split simple plugins into multiple actions, like RecentChanges/RecentEdits,
  MostPopular/LeastPopular, AllPages/AllPagesCreatedByMe/AllPagesLastEditedByMe/
  AllPagesOwnedByMe which differ only in one argument.
# Simplify the syntax for actions on another actions using a ~PageList
  as result of an actionpage as input parameter for another action or
  format.

* Those actions which have buttons or links in the theme or are
  referenced in the standard pgsrc pageset require their
  (possibly localized) actionpages, otherwise the actions will not work.
* If the localized actionpage is not found the english version is
  used.
* If no actionpage is found, it is recommended to do action=upgrade,
  which imports all missing and required action pages into the database.

So for a hypothetical new ~MyActionPage plugin ~MyActionPage will
invoke the plugin and ~Help:~MyActionPagePlugin should be the description page.

== Existing Plugins ==

See [[PluginManager]] for a detailed list. Most plugins should have their
own description page as subpage of **Help/** with the name **Plugin**
appended.

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[[PhpWikiDocumentation]]