### compiler
-As a compiler, starts by calling the `refresh` hook. Then it checks
-the wiki's source to find new or changed pages. The `needsbuild` hook is
-then called to allow manipulation of the list of pages that need to be
-built.
-
-Now that it knows what pages it needs to build, ikiwiki runs two
-compile passes. First, it runs `scan` hooks, which collect metadata about
-the pages. Then it runs a page rendering pipeline, by calling in turn these
-hooks: `filter`, `preprocess`, `linkify`, `htmlize`, `postscan`,
-`pagetemplate`, `sanitize`, `format`.
-
-After all necessary pages are built, it calls the `change` hook. Finally,
-if a page is was deleted, the `delete` hook is called, and the files that
-page had previously produced are removed.
+As a compiler, ikiwiki starts by calling the
+[[`refresh`|plugins/write#refresh]] hook. Then it checks the wiki's source to
+find new or changed pages. The [[`needsbuild`|plugins/write#needsbuild]] hook
+is then called to allow manipulation of the list of pages that need to be
+built.
+
+Now that it knows what pages it needs to build, ikiwiki runs two compile
+passes. First, it runs [[`scan`|plugins/write#scan]] hooks, which collect
+metadata about the pages. Then it runs a page rendering pipeline, by calling
+in turn these hooks: [[`filter`|plugins/write#filter]],
+[[`preprocess`|plugins/write#preprocess]],
+[[`linkify`|plugins/write#linkify]], [[`htmlize`|plugins/write#htmlize]],
+[[`indexhtml`|plugins/write#indexhtml]],
+[[`pagetemplate`|plugins/write#pagetemplate]],
+[[`sanitize`|plugins/write#sanitize]], [[`format`|plugins/write#format]].
+
+After all necessary pages are built, it calls the
+[[`changes`|plugins/write#changes]] hook. Finally, if a page was deleted, the
+[[`delete`|plugins/write#delete]] hook is called, and the files that page had
+previously produced are removed.
### cgi
-The flow between hooks when ikiwiki is run as a cgi is best illistrated by
+The flow between hooks when ikiwiki is run as a cgi is best illustrated by
an example.
-* *Alice browses to a page and clicks Edit.*
-* Ikiwiki is run as a cgi. It assigns Alice a session cookie, and,
- by calling the `auth` hooks, sees that she is not yet logged in.
-* The `sessioncgi` hooks are then called, and one of them,
- from the [[editpage]] plugin, notices that the cgi has been told "do=edit".
-* The [[editpage]] plugin calls the `canedit` hook to check if this
- page edit is allowed. The [[signinedit]] plugin has a hook that says not:
- Alice is not signed in.
-* The [[signinedit]] plugin then launches the signin process. A signin
- page is built by calling the `formbuilder_setup` hook.
-* *Alice signs in with her openid.*
-* The [[openid]] plugin's `formbuilder` hook sees that an openid was
- entered in the signin form, and redirects to Alice's openid provider.
-* Alice's openid provider calls back to ikiwiki. The [[openid]] plugin
- has an `auth` hook that finishes the openid signin process.
+Alice browses to a page and clicks Edit.
+
+* Ikiwiki is run as a cgi. It assigns Alice a session cookie, and, by calling
+ the [[`auth`|plugins/write#auth]] hooks, sees that she is not yet logged in.
+* The [[`sessioncgi`|plugins/write#sessioncgi]] hooks are then called, and one
+ of them, from the [[editpage]] plugin, notices that the cgi has been told
+ "do=edit".
+* The [[editpage]] plugin calls the [[`canedit`|plugins/write#canedit]] hook
+ to check if this page edit is allowed. The [[signinedit]] plugin has a hook
+ that says not: Alice is not signed in.
+* The [[signinedit]] plugin then launches the signin process. A signin page is
+ built by calling the [[`formbuilder_setup`|plugins/write#formbuilder]]
+ hook.
+
+Alice signs in with her openid.
+
+* The [[openid]] plugin's [[`formbuilder`|plugins/write#formbuilder]] hook
+ sees that an openid was entered in the signin form, and redirects to Alice's
+ openid provider.
+* Alice's openid provider calls back to ikiwiki. The [[openid]] plugin has an
+ [[`auth`|plugins/write#auth]] hook that finishes the openid signin process.
* Signin complete, ikiwiki returns to what Alice was doing before; editing
a page.
-* Now all the `canedit` hooks are happy. The [[editpage]] plugin calls
- `formbuilder_setup` to display the page editing form.
-* *Alice saves her change to the page.*
-* The [[editpage]] plugin's `formbuilder` hook sees that the Save button
- was pressed, and calls the `checkcontent` and `editcontent` hooks.
- Then it saves the page to disk, and branches into the compiler part
- of ikiwiki to refresh the wiki.
+* Now all the [[`canedit`|plugins/write#canedit]] hooks are happy. The
+ [[editpage]] plugin calls
+ [[`formbuilder_setup`|plugins/write#formbuilder]] to display the page
+ editing form.
+
+Alice saves her change to the page.
+
+* The [[editpage]] plugin's [[`formbuilder`|plugins/write#formbuilder]] hook
+ sees that the Save button was pressed, and calls the
+ [[`checkcontent`|plugins/write#checkcontent]] and
+ [[`editcontent`|plugins/write#editcontent]] hooks. Then it saves the page
+ to disk, and branches into the compiler part of ikiwiki to refresh the wiki.
## Types of plugins
The function is passed no values. It's ok for the function to call
`error()` if something isn't configured right.
-### refresh
+### <a name="refresh">refresh</a>
hook(type => "refresh", id => "foo", call => \&refresh);
It's useful for plugins that need to create or modify a source page. The
function is passed no values.
-### needsbuild
+### <a name="needsbuild">needsbuild</a>
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 files that will be rebuilt, and can modify the array, either
-adding or removing files from it.
+This allows a plugin to observe or even manipulate the list of files that
+need to be built when the wiki is refreshed.
+
+As its first parameter, the function is passed a reference to an array of
+files that will be built. It should return an array reference that is a
+modified version of its input. It can add or remove files from it.
-### scan
+The second parameter passed to the function is a reference to an array of
+files that have been deleted.
+
+### <a name="scan">scan</a>
hook(type => "scan", id => "foo", call => \&scan);
The function is passed named parameters "page" and "content". Its return
value is ignored.
-### filter
+### <a name="readtemplate">readtemplate</a>
+
+ hook(type => "readtemplate", id => "foo", call => \&readtemplate);
+
+Runs on the raw source of a page or `*.tmpl` file that is being
+used as a template, before it is parsed by [[!cpan HTML::Template]].
+For instance, the [[plugins/templatebody]] plugin uses this to return
+the content of the [[ikiwiki/directive/templatebody]] directive (if there
+is one) instead of the page's full content.
+
+The function is passed named parameters:
+
+* `id`: the name under which the template was looked up,
+ such as `page.tmpl` or `note`
+* `page`: the name of the template as a page or attachment in the wiki,
+ such as `templates/note`, or `undef` if it's outside the wiki (e.g. in
+ `/usr/share/ikiwiki/templates`)
+* `content`: the content of the corresponding file
+* `untrusted`: true if the template was loaded from the wiki or an underlay,
+ false if it was loaded from a trusted location
+
+It should return the replacement content.
+
+### <a name="filter">filter</a>
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",
+Runs on the full raw source of a page, before anything else touches it, and
+can make arbitrary changes. The function is passed named parameters "page",
"destpage", and "content". It should return the filtered content.
-### preprocess
+### <a name="preprocess">preprocess</a>
Adding a preprocessor [[ikiwiki/directive]] is probably the most common use
of a plugin.
be linkified and passed through markdown (or whatever engine is used to
htmlize the page) along with the rest of the page.
-### linkify
+### <a name="linkify">linkify</a>
hook(type => "linkify", id => "foo", call => \&linkify);
for the links on the page and adds them to `%links` (typically by calling
`add_link`).
-### htmlize
+### <a name="htmlize">htmlize</a>
hook(type => "htmlize", id => "ext", call => \&htmlize);
If `hook` is passed an optional "longname" parameter, this value is used
when prompting a user to choose a page type on the edit page form.
-### postscan
+### <a name="indexhtml">indexhtml</a>
- hook(type => "postscan", id => "foo", call => \&postscan);
+ hook(type => "indexhtml", id => "foo", call => \&indexhtml);
This hook is called once the page has been converted to html (but before
the generated html is put in a template). The most common use is to
update search indexes. Added in ikiwiki 2.54.
-The function is passed named parameters "page" and "content". Its return
-value is ignored.
+The function is passed named parameters "page", "destpage", and "content".
+Its return value is ignored.
-### pagetemplate
+### <a name="pagetemplate">pagetemplate</a>
hook(type => "pagetemplate", id => "foo", call => \&pagetemplate);
-[[Templates|wikitemplates]] are filled out for many different things in
+[[Templates]] 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
hook(type => "templatefile", id => "foo", call => \&templatefile);
-This hook allows plugins to change the [[template|wikitemplates]] that is
+This hook allows plugins to change the [[template|templates]] 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.
+should return the name of the template file to use (relative to the
+template directory), or undef if it doesn't want to change the default
+("page.tmpl").
+
+### pageactions
-### sanitize
+ hook(type => "pageactions", id => "foo", call => \&pageactions);
+
+This hook allows plugins to add arbitrary actions to the action bar on a
+page (next to Edit, RecentChanges, etc). The hook is passed a "page"
+parameter, and can return a list of html fragments to add to the action
+bar.
+
+### <a name="sanitize">sanitize</a>
hook(type => "sanitize", id => "foo", call => \&sanitize);
The function is passed named parameters: "page", "destpage", and "content",
and should return the sanitized content.
-### format
+### <a name="format">format</a>
hook(type => "format", id => "foo", call => \&format);
The function is passed named parameters: "page" and "content", and
should return the formatted content.
-### delete
+### build_affected
+
+ hook(type => "build_affected", id => "foo", call => \&build_affected);
+
+This hook is called after the directly changed pages have been built,
+and can cause extra pages to be built. If links and backlinks were provided
+by a plugin, this would be where that plugin would rebuild pages whose
+backlinks have changed, for instance. The [[trail]] plugin uses this hook
+to rebuild pages whose next or previous page has changed.
+
+The function should currently ignore its parameters. It returns a list with
+an even number of items (a hash in list context), where the first item of
+each pair is a page name to be rebuilt (if it was not already rebuilt), and
+the second is a log message resembling
+`building plugins/write because the phase of the moon has changed`.
+
+### <a name="delete">delete</a>
hook(type => "delete", id => "foo", call => \&delete);
-Each time a page or pages is removed from the wiki, the referenced function
+After a page or pages is removed from the wiki, the referenced function
is called, and passed the names of the source files that were removed.
-### change
+### rendered
- hook(type => "change", id => "foo", call => \&render);
+ hook(type => "rendered", id => "foo", call => \&rendered);
-Each time ikiwiki renders a change or addition (but not deletion) to the
+After ikiwiki renders a change or addition (but not deletion) to the
wiki, the referenced function is called, and passed the names of the
source files that were rendered.
+(This hook used to be called "change", but that was not accurate.
+For now, plugins using the old hook name will still work.)
+
+### <a name="changes">changes</a>
+
+ hook(type => "changes", id => "foo", call => \&changes);
+
+After ikiwiki renders changes to the wiki, the referenced function is
+called, and passed the names of the source files that were added, modified,
+or deleted.
+
### cgi
hook(type => "cgi", id => "foo", call => \&cgi);
Note that cgi hooks are called as early as possible, before any ikiwiki
state is loaded, and with no session information.
-### auth
+### <a name="auth">auth</a>
hook(type => "auth", id => "foo", call => \&auth);
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
+Auth plugins can use the loginselector helper plugin to let the user
+select which authentication method to use.
+
+### <a name="sessioncgi">sessioncgi</a>
hook(type => "sessioncgi", id => "foo", call => \&sessioncgi);
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
+### <a name="canedit">canedit</a>
hook(type => "canedit", id => "foo", call => \&canedit);
but is passed the named parameters `cgi` (a CGI object), `session` (a
session object), `src`, `srcfile`, `dest` and `destfile`.
-### checkcontent
+### <a name="checkcontent">checkcontent</a>
hook(type => "checkcontent", id => "foo", call => \&checkcontent);
that can be run to perform whatever action is necessary to allow the user
to post the content.
-### editcontent
+### <a name="editcontent">editcontent</a>
hook(type => "editcontent", id => "foo", call => \&editcontent);
It can modify the content as desired, and should return the content.
-### formbuilder
+### <a name="formbuilder">formbuilder</a>
hook(type => "formbuilder_setup", id => "foo", call => \&formbuilder_setup);
hook(type => "formbuilder", id => "foo", call => \&formbuilder);
describing the option. There can also be an item named "plugin", which
describes the plugin as a whole. For example:
- return
+ return
plugin => {
description => "description of this plugin",
safe => 1,
* `description` is a short description of the option.
* `link` is a link to further information about the option. This can either
be a [[ikiwiki/WikiLink]], or an url.
+* `htmldescription` is displayed instead of the description by websetup.
* `advanced` can be set to true if the option is more suitable for advanced
users.
* `safe` should be false if the option should not be displayed in unsafe
strictly required.
* `section` can optionally specify which section in the config file
the plugin fits in. The convention is to name the sections the
- same as the tags used for [[plugins|plugin]] on this wiki.
+ same as the tags used for [[plugins]] on this wiki.
### genwrapper
hook(type => "genwrapper", id => "foo", call => \&genwrapper);
This hook is used to inject C code (which it returns) into the `main`
-function of the ikiwiki wrapper when it is being generated.
+function of the ikiwiki wrapper when it is being generated.
+
+The code runs before anything else -- in particular it runs before
+the suid wrapper has sanitized its environment.
+
+### disable
+
+ hook(type => "disable", id => "foo", call => \&disable);
+
+This hook is only run when a previously enabled plugin gets disabled
+during ikiwiki setup. Plugins can use this to perform cleanups.
## Exported variables
The `%wikistate` hash can be used by a plugin to store persistant state
that is not bound to any one page. To set a value, use
-`$wikistate{$id}{$key}=$value, where `$value` is anything Storable can
+`$wikistate{$id}{$key}=$value`, where `$value` is anything Storable can
serialize, `$key` is any string you like, and `$id` must be the same as the
"id" parameter passed to `hook()` when registering the plugin, so that the
state can be dropped if the plugin is no longer used.
$links{"foo"} = ["bar", "baz"];
+### `%typedlinks`
+
+The `%typedlinks` hash records links of specific types. Do not modify this
+hash directly; call `add_link()`. The keys are page names, and the values
+are hash references. In each page's hash reference, the keys are link types
+defined by plugins, and the values are hash references with link targets
+as keys, and 1 as a dummy value, something like this:
+
+ $typedlinks{"foo"} = {
+ tag => { short_word => 1, metasyntactic_variable => 1 },
+ next_page => { bar => 1 },
+ };
+
+Ordinary [[WikiLinks|ikiwiki/WikiLink]] appear in `%links`, but not in
+`%typedlinks`.
+
### `%pagesources`
-The `%pagesources` has can be used to look up the source filename
+The `%pagesources` hash can be used to look up the source filename
of a page. So the key is the page name, and the value is the source
filename. Do not modify this hash.
+Attachments also appear in this hash, with the same key and value.
+
$pagesources{"foo"} = "foo.mdwn";
+ $pagesources{"logo/ikiwiki.png"} = "logo/ikiwiki.png";
+
### `%destsources`
The `%destsources` hash records the name of the source file used to
create each destination file. The key is the output filename (ie,
-"foo/index.html"), and the value is the source filename that it was built
-from (eg, "foo.mdwn"). Note that a single source file may create multiple
+"foo/index.html"), and the value is the name of the page that it was built
+from (eg, "foo"). Note that a single source file may create multiple
destination files. Do not modify this hash directly; call `will_render()`.
-
- $destsources{"foo/index.html"} = "foo.mdwn";
+
+Attachments also appear in this hash, with the same key and value.
+
+ $destsources{"foo/index.html"} = "foo";
+ $destsources{"logo/ikiwiki.png"} = "logo/ikiwiki.png";
## Library functions
### `template($;@)`
-Creates and returns a [[!cpan HTML::Template]] object. The first parameter
-is the name of the file in the template directory. The optional remaining
+Creates and returns a [[!cpan HTML::Template]] object. (In a list context,
+returns the parameters needed to construct the obhect.)
+
+The first parameter is the name of the template file. The optional remaining
parameters are passed to `HTML::Template->new`.
+Normally, the template file is first looked for in the templates/ subdirectory
+of the srcdir. Failing that, it is looked for in the templatedir.
+
+Wiki pages can be used as templates. This should be done only for templates
+which it is safe to let wiki users edit. Enable it by passing a filename
+with no ".tmpl" extension. Template pages are normally looked for in
+the templates/ directory. If the page name starts with "/", a page
+elsewhere in the wiki can be used.
+
+If the template is not found, or contains a syntax error, an error is thrown.
+
+### `template_depends($$;@)`
+
+Use this instead of `template()` if the content of a template is being
+included into a page. This causes the page to depend on the template,
+so it will be updated if the template is modified.
+
+Like `template()`, except the second parameter is the page.
+
### `htmlpage($)`
Passed a page name, returns the base name that will be used for a the html
* `filter` is a reference to a function, that is called and passed a page,
and returns true if the page should be filtered out of the list.
* `sort` specifies a sort order for the list. See
- [[ikiwiki/PageSpec/sorting]] for the avilable sort methods.
+ [[ikiwiki/PageSpec/sorting]] for the avilable sort methods. Note that
+ if a sort method is specified that depends on the
+ page content (such as 'meta(foo)'), the deptype needs to be set to
+ a content dependency.
* `reverse` if true, sorts in reverse.
* `num` if nonzero, specifies the maximum number of matching pages that
will be returned.
page will be updated whenever anything matching the PageSpec is modified.
This can be overridden by passing a `deptype` value as the third parameter.
-#### `pagespec_match($$;@)`
+### `pagespec_match($$;@)`
Passed a page name, and [[ikiwiki/PageSpec]], returns a true value if the
[[ikiwiki/PageSpec]] matches the page.
If multiple types are specified, they are combined.
-#### `bestlink($$)`
+### `bestlink($$)`
Given a page and the text of a link on the page, determine which
existing page that link best points to. Prefers pages under a
goes down the directory tree to the base looking for matching
pages, as described in [[ikiwiki/SubPage/LinkingRules]].
-#### `htmllink($$$;@)`
+### `htmllink($$$;@)`
Many plugins need to generate html links and add them to a page. This is
done by using the `htmllink` function. The usual way to call
If the directory name is not absolute, ikiwiki will assume it is in
the parent directory of the configured underlaydir.
-### `displaytime($;$)`
+### `displaytime($;$$)`
Given a time, formats it for display.
The optional second parameter is a strftime format to use to format the
time.
+If the third parameter is true, this is the publication time of a page.
+(Ie, set the html5 pubdate attribute.)
+
### `gettext`
This is the standard gettext function, although slightly optimised.
-### `urlto($$;$)`
+### `ngettext`
+
+This is the standard ngettext function, although slightly optimised.
+
+### `urlto($;$$)`
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`.
-If the third parameter is passed and is true, an absolute url will be
-constructed instead of the default relative url.
+Provide a second parameter whenever possible, since this leads to better
+behaviour for the [[plugins/po]] plugin and `file:///` URLs.
+
+If the second parameter is not specified (or `undef`), the URL will be
+valid from any page on the wiki, or from the CGI; if possible it'll
+be a path starting with `/`, but an absolute URL will be used if
+the wiki and the CGI are on different domains.
+
+If the third parameter is passed and is true, the url will be a fully
+absolute url. This is useful when generating an url to publish elsewhere.
### `newpagefile($$)`
filename of the page. For example, `targetpage("foo", "rss", "feed")`
will yield something like `foo/feed.rss`.
-### `add_link($$)`
+### `add_link($$;$)`
This adds a link to `%links`, ensuring that duplicate links are not
added. Pass it the page that contains the link, and the link text.
+An optional third parameter sets the link type. If not specified,
+it is an ordinary [[ikiwiki/WikiLink]].
+
+### `add_autofile($$$)`
+
+Sometimes you may want to add a file to the `srcdir` as a result of content
+of other pages. For example, [[plugins/tag]] pages can be automatically
+created as needed. This function can be used to do that.
+
+The three parameters are the filename to create (relative to the `srcdir`),
+the name of the plugin, and a callback function. The callback will be
+called if it is appropriate to automatically add the file, and should then
+take care of creating it, and doing anything else it needs to (such as
+checking it into revision control). Note that the callback may not always
+be called. For example, if an automatically added file is deleted by the
+user, ikiwiki will avoid re-adding it again.
+
+This function needs to be called during the scan hook, or earlier in the
+build process, in order to add the file early enough for it to be built.
+
## Miscellaneous
### Internal use pages
it might return the current revision ID of the file, and use that
information later when merging changes.
-#### `rcs_commit($$$;$$)`
+#### `rcs_commit(@)`
+
+Passed named parameters: `file`, `message`, `token` (from `rcs_prepedit`),
+and `session` (optional).
-Passed a file, message, token (from `rcs_prepedit`), user, and ip address.
Should try to commit the file. Returns `undef` on *success* and a version
of the page with the rcs's conflict markers on failure.
-#### `rcs_commit_staged($$$)`
+#### `rcs_commit_staged(@)`
+
+Passed named parameters: `message`, and `session` (optional).
-Passed a message, user, and ip address. Should commit all staged changes.
-Returns undef on success, and an error message on failure.
+Should commit all staged changes. Returns undef on success, and an
+error message on failure.
Changes can be staged by calls to `rcs_add`, `rcs_remove`, and
`rcs_rename`.
Remove a file. The filename is relative to the root of the srcdir.
Note that this should not commit the removal, it should only prepare for it
-to be committed when `rcs_commit` (or `rcs_commit_staged`) is called. Note
-that the new file may be in a new subdir that is not yet in version
-control; the subdir can be added if so.
+to be committed when `rcs_commit` (or `rcs_commit_staged`) is called.
#### `rcs_rename($$)`
{
rev => # the RCSs id for this commit
- user => # name of user who made the change,
+ user => # user who made the change (may be an openid),
+ nickname => # short name for user (optional; not an openid),
+
committype => # either "web" or the name of the rcs,
when => # time when the change was made,
message => [
],
}
-#### `rcs_diff($)`
+#### `rcs_diff($;$)`
+
+The first parameter is the rev from `rcs_recentchanges`.
+The optional second parameter is how many lines to return (default: all).
-The parameter is the rev from `rcs_recentchanges`.
Should return a list of lines of the diff (including \n) in list
-context, and the whole diff in scalar context.
+context, and a string containing the whole diff in scalar context.
#### `rcs_getctime($)`
This is used to get the page creation time for a file from the RCS, by looking
it up in the history.
+If the RCS cannot determine a ctime for the file, return 0.
+
+#### `rcs_getmtime($)`
+
+This is used to get the page modification time for a file from the RCS, by
+looking it up in the history.
+
It's ok if this is not implemented, and throws an error.
+If the RCS cannot determine a mtime for the file, return 0.
+
#### `rcs_receive()`
This is called when ikiwiki is running as a pre-receive hook (or
It should examine the incoming changes, and do any sanity
checks that are appropriate for the RCS to limit changes to safe file adds,
-removes, and changes. If something bad is found, it should exit
-nonzero, to abort the push. Otherwise, it should return a list of
-files that were changed, in the form:
+removes, and changes. If something bad is found, it should die, to abort
+the push. Otherwise, it should return a list of files that were changed,
+in the form:
{
file => # name of file that was changed
The list will then be checked to make sure that each change is one that
is allowed to be made via the web interface.
+#### `rcs_preprevert($)`
+
+This is called by the revert web interface. It is passed a RCS-specific
+change ID, and should determine what the effects would be of reverting
+that change, and return the same data structure as `rcs_receive`.
+
+Like `rcs_receive`, it should do whatever sanity checks are appropriate
+for the RCS to limit changes to safe changes, and die if a change would
+be unsafe to revert.
+
+#### `rcs_revert($)`
+
+This is called by the revert web interface. It is passed a named
+parameter rev that is the RCS-specific change ID to revert.
+
+It should try to revert the specified rev, and leave the reversion staged
+so `rcs_commit_staged` will complete it. It should return undef on _success_
+and an error message on failure.
+
+This hook and `rcs_preprevert` are optional, if not implemented, no revert
+web interface will be available.
+
+### `rcs_find_changes($)`
+
+Finds changes committed since the passed RCS-specific rev. Returns
+a hash of the files changed, a hash of the files deleted, and the
+current rev.
+
+This hook is optional.
+
+### `rcs_get_current_rev()`
+
+Gets a RCS-specific rev, which can later be passed to `rcs_find_changes`.
+
+This hook is optional.
+
### PageSpec plugins
It's also possible to write plugins that add new functions to
they match; "created_before(foo)" is influenced by the metadata of foo;
while "glob(*)" is not influenced by the contents of any page.
+### Sorting plugins
+
+Similarly, it's possible to write plugins that add new functions as
+[[ikiwiki/pagespec/sorting]] methods. To achieve this, add a function to
+the IkiWiki::SortSpec package named `cmp_foo`, which will be used when sorting
+by `foo` or `foo(...)` is requested.
+
+The names of pages to be compared are in the global variables `$a` and `$b`
+in the IkiWiki::SortSpec package. The function should return the same thing
+as Perl's `cmp` and `<=>` operators: negative if `$a` is less than `$b`,
+positive if `$a` is greater, or zero if they are considered equal. It may
+also raise an error using `error`, for instance if it needs a parameter but
+one isn't provided.
+
+The function will also be passed one or more parameters. The first is
+`undef` if invoked as `foo`, or the parameter `"bar"` if invoked as `foo(bar)`;
+it may also be passed additional, named parameters.
+
### Setup plugins
The ikiwiki setup file is loaded using a pluggable mechanism. If you look