X-Git-Url: http://git.vanrenterghem.biz/git.ikiwiki.info.git/blobdiff_plain/54898d16d4c86fddcb1b5588eac67a729c14deeb..3fe434189b99daf3d8cc075186c4ed4ebdd43b8f:/doc/plugins/write.mdwn

diff --git a/doc/plugins/write.mdwn b/doc/plugins/write.mdwn
index 1407b5a12..95f4a39df 100644
--- a/doc/plugins/write.mdwn
+++ b/doc/plugins/write.mdwn
@@ -31,20 +31,26 @@ is accomplished by calling various hooks provided by plugins.
 
 ### compiler
 
-As a compiler, ikiwiki 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
 
@@ -53,33 +59,39 @@ 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.
+* 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` 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.
+* 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.
+* 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` 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.
+* 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
 
@@ -165,7 +177,7 @@ is populated at this point, but other state has not yet been loaded.
 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);
 
@@ -173,16 +185,21 @@ 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
+### <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.
+
+The second parameter passed to the function is a reference to an array of
+files that have been deleted.
 
-### scan
+### <a name="scan">scan</a>
 
 	hook(type => "scan", id => "foo", call => \&scan);
 
@@ -194,15 +211,38 @@ them to `%links`. Present in IkiWiki 2.40 and later.
 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.
@@ -245,7 +285,7 @@ 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
+### <a name="linkify">linkify</a>
 
 	hook(type => "linkify", id => "foo", call => \&linkify);
 
@@ -258,7 +298,7 @@ Plugins that implement linkify must also implement a scan hook, that scans
 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);
 
@@ -282,22 +322,22 @@ like `Makefile` that have no extension.
 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
@@ -313,13 +353,22 @@ a new custom parameter to the template.
 
 	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 (relative to the
 template directory), or undef if it doesn't want to change the default
 ("page.tmpl").
 
-### sanitize
+### pageactions
+
+	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);
 
@@ -329,7 +378,7 @@ modify the body of a page after it has been fully converted to html.
 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);
 
@@ -342,21 +391,48 @@ when the page is being previewed.)
 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);
@@ -369,7 +445,7 @@ parameters, and if it will handle this CGI request, output a page
 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);
 
@@ -382,7 +458,10 @@ 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
+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);
 
@@ -391,7 +470,7 @@ 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
+### <a name="canedit">canedit</a>
 
 	hook(type => "canedit", id => "foo", call => \&canedit);
 
@@ -431,7 +510,7 @@ bypass it). It works exactly like the `canedit` hook,
 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);
 
@@ -452,7 +531,7 @@ should return a message stating what the problem is, or a function
 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);
 
@@ -463,7 +542,7 @@ 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
+### <a name="formbuilder">formbuilder</a>
 
 	hook(type => "formbuilder_setup", id => "foo", call => \&formbuilder_setup);
 	hook(type => "formbuilder", id => "foo", call => \&formbuilder);
@@ -566,6 +645,7 @@ describes the plugin as a whole. For example:
 * `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
@@ -579,14 +659,24 @@ describes the plugin as a whole. For example:
   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
 
@@ -620,7 +710,7 @@ wiki updates.
 
 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.
@@ -655,17 +745,24 @@ The `%pagesources` has 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
 
@@ -701,16 +798,22 @@ the entire wiki build and make the wiki unusable.
 
 ### `template($;@)`
 
-Creates and returns a [[!cpan HTML::Template]] object. The first parameter
-is the name of the template file. The optional remaining parameters are
-passed to `HTML::Template->new`.
+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.
 
-The template file is first looked for in the templates/ subdirectory of the
-srcdir. Failing that, it is looked for in the templatedir. Typically
-the filename will have a ".tmpl" extension. If a filename with no extension
-is passed, a wiki page in templates/ with its name is used as the template.
-That should only be done for templates which it is safe to let wiki users
-edit.
+If the template is not found, or contains a syntax error, an error is thrown.
 
 ### `template_depends($$;@)`
 
@@ -934,13 +1037,16 @@ search for files.
 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.
@@ -949,14 +1055,22 @@ This is the standard gettext function, although slightly optimised.
 
 This is the standard ngettext function, although slightly optimised.
 
-### `urlto($$;$)`
+### `urlto($;$$)`
 
 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($$)`
 
@@ -1035,16 +1149,20 @@ token, that will be passed into `rcs_commit` when committing. For example,
 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 a message, user, and ip address. Should commit all staged changes.
-Returns undef on success, and an error message on failure.
+Passed named parameters: `message`, and `session` (optional).
+
+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`.
@@ -1064,9 +1182,7 @@ to version control; the subdir can be added if so.
 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($$)`
 
@@ -1087,7 +1203,9 @@ The data structure returned for each change is:
 
 	{
 		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 => [
@@ -1104,19 +1222,19 @@ The data structure returned for each change is:
 		],
 	}
 
-#### `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.
 
-It's ok if this is not implemented, and throws an error.
-
 If the RCS cannot determine a ctime for the file, return 0.
 
 #### `rcs_getmtime($)`
@@ -1137,9 +1255,9 @@ sense to implement for all RCSs.
 
 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
@@ -1152,6 +1270,42 @@ files that were changed, in the form:
 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