Merge branch 'master' of ssh://git.ikiwiki.info/srv/git/ikiwiki.info

[git.ikiwiki.info.git] / doc / plugins / write.mdwn

diff --git a/doc/plugins/write.mdwn b/doc/plugins/write.mdwn
index 8886bca29051c68e9b363b4e3e22bc72d73f231b..b9d7c01c2367147b3c7771ca312e8a5b3193e82e 100644 (file)
--- a/doc/plugins/write.mdwn
+++ b/doc/plugins/write.mdwn
@@ -1,11 +1,36 @@
-ikiwiki [[plugins]] are written in perl. Each plugin is a perl module, in
-the `IkiWiki::Plugin` namespace. The name of the plugin is typically in
-lowercase, such as `IkiWiki::Plugin::inline`. Ikiwiki includes a
-`IkiWiki::Plugin::skeleton` that can be fleshed out to make a useful
-plugin. `IkiWiki::Plugin::pagecount` is another simple example.
+Ikiwiki's plugin interface allows all kinds of useful [[plugins]] to be
+written to extend ikiwiki in many ways. Despite the length of this page,
+it's not really hard. This page is a complete reference to everything a
+plugin might want to do. There is also a quick [[tutorial]].

 
 [[toc levels=2]]
 
 
 [[toc levels=2]]
 

+## Types of plugins
+
+Most ikiwiki [[plugins]] are written in perl, like ikiwiki. This gives the
+plugin full access to ikiwiki's internals, and is the most efficient.
+However, plugins can actually be written in any language that supports XML
+RPC. These are called [[external]] plugins.
+
+A plugin written in perl is a perl module, in the `IkiWiki::Plugin`
+namespace. The name of the plugin is typically in lowercase, such as
+`IkiWiki::Plugin::inline`. Ikiwiki includes a `IkiWiki::Plugin::skeleton`
+that can be fleshed out to make a useful plugin.
+`IkiWiki::Plugin::pagecount` is another simple example. All perl plugins
+should `use IkiWiki` to import the ikiwiki plugin interface. It's a good
+idea to include the version number of the plugin interface that your plugin
+expects: `use IkiWiki 2.00`.
+
+An external plugin is an executable program. It can be written in any
+language. Its interface to ikiwiki is via XML RPC, which it reads from
+ikiwiki on its standard input, and writes to ikiwiki on its standard
+output. For more details on writing external plugins, see [[external]].
+
+Despite these two types of plugins having such different interfaces,
+they're the same as far as how they hook into ikiwiki. This document will
+explain how to write both sorts of plugins, albeit with an emphasis on perl
+plugins.
+

 ## Considerations
 
 One thing to keep in mind when writing a plugin is that ikiwiki is a wiki
 ## Considerations
 
 One thing to keep in mind when writing a plugin is that ikiwiki is a wiki


@@ -19,16 +44,17 @@ being edited.
 
 ## Registering plugins
 
 
 ## Registering plugins
 

-All plugins should `use IkiWiki` to import the ikiwiki plugin interface.
-

 Plugins should, when imported, call `hook()` to hook into ikiwiki's
 processing. The function uses named parameters, and use varies depending on
 the type of hook being registered -- see below. Note that a plugin can call
 the function more than once to register multiple hooks. All calls to
 `hook()` should be passed a "type" parameter, which gives the type of
 hook, a "id" paramter, which should be a unique string for this plugin, and
 Plugins should, when imported, call `hook()` to hook into ikiwiki's
 processing. The function uses named parameters, and use varies depending on
 the type of hook being registered -- see below. Note that a plugin can call
 the function more than once to register multiple hooks. All calls to
 `hook()` should be passed a "type" parameter, which gives the type of
 hook, a "id" paramter, which should be a unique string for this plugin, and

-a "call" parameter, which is a reference to a function to call for the
-hook.
+a "call" parameter, which tells what function to call for the hook.
+
+An optional "last" parameter, if set to a true value, makes the hook run
+after all other hooks of its type. Useful if the hook depends on some other
+hook being run first.

 
 ## Types of hooks
 
 
 ## Types of hooks
 


@@ -56,18 +82,35 @@ configuration. It's called early in the startup process. The
 function is passed no values. It's ok for the function to call
 `error()` if something isn't configured right.
 
 function is passed no values. It's ok for the function to call
 `error()` if something isn't configured right.
 

+### refresh
+
+       hook(type => "refresh", id => "foo", call => \&refresh);
+
+This hook is called just before ikiwiki scans the wiki for changed files.
+It's useful for plugins that need to create or modify a source page. The
+function is passed no values.
+
+### needsbuild
+
+       hook(type => "needsbuild", id => "foo", call => \&needsbuild);
+
+This allows a plugin to manipulate the list of files that need to be
+built when the wiki is refreshed. The function is passed a reference to an
+array of pages that will be rebuilt, and can modify the array, either
+adding or removing files from it.
+

 ### filter
 
        hook(type => "filter", id => "foo", call => \&filter);
 
 Runs on the raw source of a page, before anything else touches it, and can
 ### filter
 
        hook(type => "filter", id => "foo", call => \&filter);
 
 Runs on the raw source of a page, before anything else touches it, and can

-make arbitrary changes. The function is passed named parameters `page` and
-`content` and should return the filtered content.
+make arbitrary changes. The function is passed named parameters "page",
+"destpage", and "content". It should return the filtered content.

 
 ### preprocess
 
 
 ### preprocess
 

-Adding a [[PreProcessorDirective]] is probably the most common use of a
-plugin.
+Adding a [[ikiwiki/PreProcessorDirective]] is probably the most common use
+of a plugin.

 
         hook(type => "preprocess", id => "foo", call => \&preprocess);
 
 
         hook(type => "preprocess", id => "foo", call => \&preprocess);
 


@@ -77,17 +120,49 @@ the preprocessor directive.
 Each time the directive is processed, the referenced function (`preprocess`
 in the example above) is called, and is passed named parameters. A "page"
 parameter gives the name of the page that embedded the preprocessor
 Each time the directive is processed, the referenced function (`preprocess`
 in the example above) is called, and is passed named parameters. A "page"
 parameter gives the name of the page that embedded the preprocessor

-directive, while a "destpage" parameter gices the name of the page the
-content is going to (different for inlined pages). All parameters included
-in the directive are included as named parameters as well. Whatever the
-function returns goes onto the page in place of the directive.
+directive, while a "destpage" parameter gives the name of the page the
+content is going to (different for inlined pages), and a "preview"
+parameter is set to a true value if the page is being previewed. All
+parameters included in the directive are included as named parameters as
+well. Whatever the function returns goes onto the page in place of the
+directive.
+
+An optional "scan" parameter, if set to a true value, makes the hook be
+called during the preliminary scan that ikiwiki makes of updated pages,
+before begining to render pages. This parameter should be set to true if
+the hook modifies data in `%links`. Note that doing so will make the hook
+be run twice per page build, so avoid doing it for expensive hooks. (As an
+optimisation, if your preprocessor hook is called in a void contets, you
+can assume it's being run in scan mode.)

 
 Note that if the [[htmlscrubber]] is enabled, html in
 
 Note that if the [[htmlscrubber]] is enabled, html in

-[[PreProcessorDirective]] output is sanitised, which may limit what your
-plugin can do. Also, the rest of the page content is not in html format at
-preprocessor time. Text output by a preprocessor directive will be
-linkified and passed through markdown (or whatever engine is used to htmlize
-the page) along with the rest of the page.
+[[ikiwiki/PreProcessorDirective]] output is sanitised, which may limit what
+your plugin can do. Also, the rest of the page content is not in html
+format at preprocessor time. Text output by a preprocessor directive will
+be linkified and passed through markdown (or whatever engine is used to
+htmlize the page) along with the rest of the page.
+
+### linkify
+
+       hook(type => "linkify", id => "foo", call => \&linkify);
+
+This hook is called to convert [[WikiLinks|WikiLink]] on the page into html
+links. The function is passed named parameters "page", "destpage", and
+"content". It should return the linkified content.
+
+Plugins that implement linkify must also implement a scan hook, that scans
+for the links on the page and adds them to `%links`.
+
+### scan
+
+       hook(type => "scan", id => "foo", call => \&scan);
+
+This hook is called early in the process of building the wiki, and is used
+as a first pass scan of the page, to collect metadata about the page. It's
+mostly used to scan the page for WikiLinks, and add them to `%links`.
+
+The function is passed named parameters "page" and "content". Its return
+value is ignored.

 
 ### htmlize
 
 
 ### htmlize
 


@@ -105,17 +180,28 @@ return the htmlized content.
 
        hook(type => "pagetemplate", id => "foo", call => \&pagetemplate);
 
 
        hook(type => "pagetemplate", id => "foo", call => \&pagetemplate);
 

-Each time a page (or part of a blog page, or an rss feed) is rendered, a
-[[template|templates]] is filled out. This hook allows modifying that
-template. The function is passed named parameters. The "page" and
+[[Templates|wikitemplates]] are filled out for many different things in
+ikiwiki, like generating a page, or part of a blog page, or an rss feed, or
+a cgi. This hook allows modifying the variables available on those
+templates. The function is passed named parameters. The "page" and

 "destpage" parameters are the same as for a preprocess hook. The "template"
 "destpage" parameters are the same as for a preprocess hook. The "template"

-parameter is a `HTML::Template` object that is the template that will be
-used to generate the page. The function can manipulate that template
-object.
+parameter is a [[cpan HTML::Template]] object that is the template that
+will be used to generate the page. The function can manipulate that
+template object.

 
 

-The most common thing to do is probably to call $template->param() to add
+The most common thing to do is probably to call `$template->param()` to add

 a new custom parameter to the template.
 
 a new custom parameter to the template.
 

+### templatefile
+
+       hook(type => "templatefile", id => "foo", call => \&templatefile);
+
+This hook allows plugins to change the [[template|wikitemplates]] that is
+used for a page in the wiki. The hook is passed a "page" parameter, and
+should return the name of the template file to use, or undef if it doesn't
+want to change the default ("page.tmpl"). Template files are looked for in
+/usr/share/ikiwiki/templates by default.
+

 ### sanitize
 
        hook(type => "sanitize", id => "foo", call => \&sanitize);
 ### sanitize
 
        hook(type => "sanitize", id => "foo", call => \&sanitize);


@@ -158,8 +244,84 @@ source files that were rendered.
 
 Use this to hook into ikiwiki's cgi script. Each registered cgi hook is
 called in turn, and passed a CGI object. The hook should examine the
 
 Use this to hook into ikiwiki's cgi script. Each registered cgi hook is
 called in turn, and passed a CGI object. The hook should examine the

-parameters, and if it will handle this CGI request, output a page and
-terminate the program.
+parameters, and if it will handle this CGI request, output a page
+(including the http headers) and terminate the program.
+
+Note that cgi hooks are called as early as possible, before any ikiwiki
+state is loaded, and with no session information.
+
+### auth
+
+       hook(type => "auth", id => "foo", call => \&auth);
+
+This hook can be used to implement a different authentication method than
+the standard web form. When a user needs to be authenticated, each registered
+auth hook is called in turn, and passed a CGI object and a session object. 
+
+If the hook is able to authenticate the user, it should set the session
+object's "name" parameter to the authenticated user's name. Note that
+if the name is set to the name of a user who is not registered,
+a basic registration of the user will be automatically performed.
+
+### sessioncgi
+
+       hook(type => "sessioncgi", id => "foo", call => \&sessioncgi);
+
+Unlike the cgi hook, which is run as soon as possible, the sessioncgi hook
+is only run once a session object is available. It is passed both a CGI
+object and a session object. To check if the user is in fact signed in, you
+can check if the session object has a "name" parameter set.
+
+### canedit
+
+       hook(type => "canedit", id => "foo", call => \&pagelocked);
+
+This hook can be used to implement arbitrary access methods to control when
+a page can be edited using the web interface (commits from revision control
+bypass it). When a page is edited, each registered canedit hook is called
+in turn, and passed the page name, a CGI object, and a session object.
+
+If the hook has no opinion about whether the edit can proceed, return
+`undef`, and the next plugin will be asked to decide. If edit can proceed,
+the hook should return "". If the edit is not allowed by this hook, the
+hook should return an error message for the user to see, or a function 
+that can be run to log the user in or perform other action necessary for
+them to be able to edit the page.
+
+This hook should avoid directly redirecting the user to a signin page,
+since it's sometimes used to test to see which pages in a set of pages a
+user can edit.
+
+### editcontent
+
+       hook(type => "editcontent", id => "foo", call => \&editcontent);
+
+This hook is called when a page is saved (or previewed) using the web
+interface. It is passed named parameters: `content`, `page`, `cgi`, and
+`session`. These are, respectively, the new page content as entered by the
+user, the page name, a `CGI` object, and the user's `CGI::Session`. 
+
+It can modify the content as desired, and should return the content.
+
+### formbuilder
+
+       hook(type => "formbuilder_setup", id => "foo", call => \&formbuilder_setup);
+       hook(type => "formbuilder", id => "foo", call => \&formbuilder);
+
+These hooks allow tapping into the parts of ikiwiki that use [[cpan
+CGI::FormBuilder]] to generate web forms. These hooks are passed named
+parameters: `cgi`, `session`, `form`, and `buttons`. These are, respectively,
+the `CGI` object, the user's `CGI::Session`, a `CGI::FormBuilder`, and a
+reference to an array of names of buttons to go on the form.
+
+Each time a form is set up, the `formbuilder_setup` hook is called.
+Typically the `formbuilder_setup` hook will check the form's title, and if
+it's a form that it needs to modify, will call various methods to
+add/remove/change fields, tweak the validation code for the fields, etc. It
+will not validate or display the form.
+
+Just before a form is displayed to the user, the `formbuilder` hook is
+called. It can be used to validate the form, but should not display it.

 
 ### savestate
 
 
 ### savestate
 


@@ -173,14 +335,14 @@ they're saved, etc.
 
 To import the ikiwiki plugin interface:
 
 
 To import the ikiwiki plugin interface:
 

-       use IkiWiki;
+       use IkiWiki '1.00';

 
 This will import several variables and functions into your plugin's
 namespace. These variables and functions are the ones most plugins need,
 and a special effort will be made to avoid changing them in incompatible
 ways, and to document any changes that have to be made in the future.
 
 
 This will import several variables and functions into your plugin's
 namespace. These variables and functions are the ones most plugins need,
 and a special effort will be made to avoid changing them in incompatible
 ways, and to document any changes that have to be made in the future.
 

-Note that IkiWiki also provides other variables functions that are not
+Note that IkiWiki also provides other variables and functions that are not

 exported by default. No guarantee is made about these in the future, so if
 it's not exported, the wise choice is to not use it.
 
 exported by default. No guarantee is made about these in the future, so if
 it's not exported, the wise choice is to not use it.
 


@@ -190,6 +352,23 @@ A plugin can access the wiki's configuration via the `%config`
 hash. The best way to understand the contents of the hash is to look at
 [[ikiwiki.setup]], which sets the hash content to configure the wiki.
 
 hash. The best way to understand the contents of the hash is to look at
 [[ikiwiki.setup]], which sets the hash content to configure the wiki.
 

+### %pagestate
+
+The `%pagestate` hash can be used by plugins to save state that they will need
+next time ikiwiki is run. The hash holds per-page state, so to set a value,
+use `%pagestate{$page}{$id}{$key}=$value`, and to retrieve the value,
+use `%pagestate{$page}{$id}{$key}`.
+
+`$key` can be any string you like, but `$id` must be the same as the "id"
+parameter passed to `hook()` when registering the plugin. This is so
+ikiwiki can know when to delete pagestate for plugins that are no longer
+used.
+
+When pages are deleted, ikiwiki automatically deletes their pagestate too.
+
+Note that page state does not persist across wiki rebuilds, only across
+wiki updates.
+

 ### Other variables
 
 If your plugin needs to access data about other pages in the wiki. It can
 ### Other variables
 
 If your plugin needs to access data about other pages in the wiki. It can


@@ -197,8 +376,12 @@ use the following hashes, using a page name as the key:
 
 * `%links` lists the names of each page that a page links to, in an array
   reference.
 
 * `%links` lists the names of each page that a page links to, in an array
   reference.

-* `%renderedfiles` contains the name of the file rendered by a page.
-* `%pagesources` contains the name of the source file for a page.
+* `%destsources` contains the name of the source file used to create each
+  destination file.
+* `%pagesources` contains the name of the source file for each page.
+
+Also, the %IkiWiki::version variable contains the version number for the
+ikiwiki program.

 
 ### Library functions
 
 
 ### Library functions
 


@@ -206,26 +389,34 @@ use the following hashes, using a page name as the key:
 
 Hook into ikiwiki's processing. See the discussion of hooks above.
 
 
 Hook into ikiwiki's processing. See the discussion of hooks above.
 

+Note that in addition to the named parameters described above, a parameter
+named `no_override` is supported, If it's set to a true value, then this hook
+will not override any existing hook with the same id. This is useful if
+the id can be controled by the user.
+

 #### `debug($)`
 
 Logs a debugging message. These are supressed unless verbose mode is turned
 on.
 
 #### `debug($)`
 
 Logs a debugging message. These are supressed unless verbose mode is turned
 on.
 

-#### `error($)`
+#### `error($;$)`

 
 

-Aborts with an error message.
+Aborts with an error message. If the second parameter is passed, it is a
+function that is called after the error message is printed, to do any final
+cleanup.

 
 Note that while any plugin can use this for a fatal error, plugins should
 try to avoid dying on bad input, as that will halt the entire wiki build
 
 Note that while any plugin can use this for a fatal error, plugins should
 try to avoid dying on bad input, as that will halt the entire wiki build

-and make the wiki unusable. So for example, if a [[PreProcessorDirective]]
-is passed bad parameters, it's better to return an error message, which can
-appear on the wiki page, rather than calling error().
+and make the wiki unusable. So for example, if a
+[[ikiwiki/PreProcessorDirective]] is passed bad parameters, it's better to
+return an error message, which can appear on the wiki page, rather than
+calling error().

 
 #### `template($;@)`
 
 
 #### `template($;@)`
 

-Creates and returns a HTML::Template object. The first parameter is the
-name of the file in the template directory. The optional remaining
-parameters are passed to HTML::Template->new.
+Creates and returns a [[cpan HTML::Template]] object. The first parameter
+is the name of the file in the template directory. The optional remaining
+parameters are passed to `HTML::Template->new`.

 
 #### `htmlpage($)`
 
 
 #### `htmlpage($)`
 


@@ -234,12 +425,17 @@ page created from it. (Ie, it appends ".html".)
 
 #### `add_depends($$)`
 
 
 #### `add_depends($$)`
 

-Makes the specified page depend on the specified [[PageSpec]].
+Makes the specified page depend on the specified [[ikiwiki/PageSpec]].
+
+#### `pagespec_match($$;@)`

 
 

-#### `pagespec_match($$)`
+Passed a page name, and [[ikiwiki/PageSpec]], returns true if the
+[[ikiwiki/PageSpec]] matches the page.

 
 

-Passed a page name, and a [[PageSpec]], returns true if the [[PageSpec]]
-matches the page.
+Additional named parameters can be passed, to further limit the match.
+The most often used is "location", which specifies the location the
+PageSpec should match against. If not passed, relative PageSpecs will match
+relative to the top of the wiki.

 
 #### `bestlink($$)`
 
 
 #### `bestlink($$)`
 


@@ -247,9 +443,9 @@ Given a page and the text of a link on the page, determine which
 existing page that link best points to. Prefers pages under a
 subdirectory with the same name as the source page, failing that
 goes down the directory tree to the base looking for matching
 existing page that link best points to. Prefers pages under a
 subdirectory with the same name as the source page, failing that
 goes down the directory tree to the base looking for matching

-pages, as described in [[SubPage/LinkingRules]].
+pages, as described in [[ikiwiki/SubPage/LinkingRules]].

 
 

-#### `htmllink($$$;$$$)`
+#### `htmllink($$$;@)`

 
 Many plugins need to generate html links and add them to a page. This is
 done by using the `htmllink` function. The usual way to call
 
 Many plugins need to generate html links and add them to a page. This is
 done by using the `htmllink` function. The usual way to call


@@ -266,11 +462,15 @@ Here `$destpage` is the inlining page. A `destpage` parameter is passed to
 some of the hook functions above; the ones that are not passed it are not used
 during inlining and don't need to worry about this issue.
 
 some of the hook functions above; the ones that are not passed it are not used
 during inlining and don't need to worry about this issue.
 

-The remaining three optional parameters to `htmllink` are:
+After the three required parameters, named parameters can be used to
+control some options. These are:

 
 

-1. noimageinline - set to true to avoid turning links into inline html images
-1. forcesubpage  - set to force a link to a subpage
-1. linktext - set to force the link text to something
+* noimageinline - set to true to avoid turning links into inline html images
+* forcesubpage  - set to force a link to a subpage
+* linktext - set to force the link text to something
+* anchor - set to make the link include an anchor
+* rel - set to add a rel attribute to the link
+* class - set to add a css class to the link

 
 #### `readfile($;$)`
 
 
 #### `readfile($;$)`
 


@@ -281,18 +481,40 @@ in binary mode.
 
 A failure to read the file will result in it dying with an error.
 
 
 A failure to read the file will result in it dying with an error.
 

-#### `writefile($$$;$)`
+#### `writefile($$$;$$)`

 
 Given a filename, a directory to put it in, and the file's content,
 writes a file. 
 
 
 Given a filename, a directory to put it in, and the file's content,
 writes a file. 
 

-The optional second parameter, if set to a true value, makes the file be
+The optional fourth parameter, if set to a true value, makes the file be

 written in binary mode.
 
 written in binary mode.
 

+The optional fifth parameter can be used to pass a function reference that
+will be called to handle writing to the file. The function will be called
+and passed a file descriptor it should write to, and an error recovery
+function it should call if the writing fails. (You will not normally need to
+use this interface.)
+

 A failure to write the file will result in it dying with an error.
 
 If the destination directory doesn't exist, it will first be created.
 
 A failure to write the file will result in it dying with an error.
 
 If the destination directory doesn't exist, it will first be created.
 

+#### `will_render($$)`
+
+Given a page name and a destination file name (not including the base
+destination directory), register that the page will result in that file
+being rendered. 
+
+It's important to call this before writing to any file in the destination
+directory, and it's important to call it consistently every time, even if
+the file isn't really written this time -- unless you delete any old
+version of the file. In particular, in preview mode, this should still be
+called even if the file isn't going to be written to during the preview.
+
+Ikiwiki uses this information to automatically clean up rendered files when
+the page that rendered them goes away or is changed to no longer render
+them. will_render also does a few important security checks.
+

 #### `pagetype($)`
 
 Given the name of a source file, returns the type of page it is, if it's
 #### `pagetype($)`
 
 Given the name of a source file, returns the type of page it is, if it's


@@ -306,21 +528,71 @@ that corresponds to that file.
 #### `srcfile($)`
 
 Given the name of a source file in the wiki, searches for the file in
 #### `srcfile($)`
 
 Given the name of a source file in the wiki, searches for the file in

-the source directory and the underlay directory, and returns the full
-path to the first file found.
+the source directory and the underlay directories (most recently added
+underlays first), and returns the full path to the first file found.
+
+#### `add_underlay($)`
+
+Adds a directory to the set of underlay directories that ikiwiki will
+search for files.

 
 

-#### `displaytime($)`
+If the directory name is not absolute, ikiwiki will assume it is in
+the parent directory of the configured underlaydir.
+
+#### `displaytime($;$)`

 
 Given a time, formats it for display.
 
 
 Given a time, formats it for display.
 

+The optional second parameter is a strftime format to use to format the
+time.
+
+#### `gettext`
+
+This is the standard gettext function, although slightly optimised.
+
+#### `urlto($$)`
+
+Construct a relative url to the first parameter from the page named by the
+second. The first parameter can be either a page name, or some other
+destination file, as registered by `will_render`.
+
+#### `targetpage($$)`
+
+Passed a page and an extension, returns the filename that page will be
+rendered to.
+
+## Internal use pages
+
+Sometimes it's useful to put pages in the wiki without the overhead of
+having them be rendered to individual html files. Such internal use pages
+are collected together to form the RecentChanges page, for example.
+
+To make an internal use page, register a filename extension that starts
+with "_". Internal use pages cannot be edited with the web interface,
+generally shouldn't contain wikilinks or preprocessor directives (use
+either on them with extreme caution), and are not matched by regular
+PageSpecs glob patterns, but instead only by a special `internal()`
+[[ikiwiki/PageSpec]].
+

 ## RCS plugins
 
 ## RCS plugins
 

-ikiwiki's support for revision control systems also uses pluggable perl
-modules. These are in the `IkiWiki::RCS` namespace, for example
+ikiwiki's support for [[revision_control_systems|rcs]] also uses pluggable
+perl modules. These are in the `IkiWiki::RCS` namespace, for example

 `IkiWiki::RCS::svn`. 
 
 `IkiWiki::RCS::svn`. 
 

-Each RCS plugin must support all the IkiWiki::rcs\_* functions.
+Each RCS plugin must support all the `IkiWiki::rcs_*` functions.

 See IkiWiki::RCS::Stub for the full list of functions. It's ok if
 See IkiWiki::RCS::Stub for the full list of functions. It's ok if

-rcs\_getctime does nothing except for throwing an error.
+`rcs_getctime` does nothing except for throwing an error.
+
+See [[RCS_details|rcs/details]] for some more info.
+
+## PageSpec plugins

 
 

-See [[about_RCS_backends]] for some more info.
+It's also possible to write plugins that add new functions to
+[[PageSpecs|ikiwiki/PageSpec]]. Such a plugin should add a function to the
+IkiWiki::PageSpec package, that is named `match_foo`, where "foo()" is
+how it will be accessed in a [[ikiwiki/PageSpec]]. The function will be passed
+two parameters: The name of the page being matched, and the thing to match
+against. It may also be passed additional, named parameters. It should return
+a IkiWiki::SuccessReason object if the match succeeds, or an
+IkiWiki::FailReason object if the match fails.