deprecate embed plugin too

I see that this plugin's lists of safe content are already well out of
date, and htmlscrubber_skip offers a non whitelist based approach, so let's
deprecate this plugin for 3.0.

debian/changelog

@@ -8,7 +8,10 @@ ikiwiki (3.00) UNRELEASED; urgency=low
     admin preferences into a setup file.
   * prefix_directives and aggregate_internal are now turned on by default.
   * ikiwiki-transition prefix_directives syntax changed
-  * googlecalendar: removed this deprecated plugin. Use embed instead.
+  * googlecalendar: removed this deprecated plugin. Use htmlscrubber_skip
+    instead.
+  * embed: This plugin is deprecated, use htmlscrubber_skip instead.
+    Closes: ##462970.
   * Version 3.00 of the plugin API.
 
  -- Joey Hess <joeyh@debian.org>  Wed, 24 Dec 2008 19:49:36 -0500

doc/plugins/embed.mdwn

@@ -13,6 +13,14 @@ In the examples below, the parts of the html that you can change are denoted
 with "XXX"; everything else must appear exactly as shown to be accepted by the
 plugin.
 
+*This plugin is deprecated.* Rather than relying on these complex lists
+of safe content, which constantly fall out of date, you're recommended to
+configure the [[htmlscrubber]] to not scrub some pages, which only trusted
+users can edit. Then you can embed anything from anywhere on those pages.
+See [[tips/embedding_content]] for details and examples.
+This plugin's lists of safe embedded content will not be maintained, and 
+the plugin will be removed in a future  release.
+
 ## google maps
 
 Use html like this to embed a map:

doc/plugins/htmlscrubber.mdwn

@@ -32,10 +32,10 @@ other HTML-related functionality, such as whether [[meta]] allows
 potentially unsafe HTML tags.
 
 The `htmlscrubber_skip` configuration setting can be used to skip scrubbing
-of some pages. Set it to a [[ikiwiki/PageSpec]], such as "!*/Discussion", and pages
-matching that can have all the evil CSS, JavsScript, and unsafe html
-elements you like. One safe way to use this is to use [[lockedit]] to lock
-those pages, so only admins can edit them.
+of some pages. Set it to a [[ikiwiki/PageSpec]], such as "!*/Discussion",
+and pages matching that can have all the evil CSS, JavsScript, and unsafe
+html elements you like. One safe way to use this is to use [[lockedit]] to
+lock those pages, so only admins can edit them.
 
 ----
 

doc/tips/embedding_content.mdwn

@@ -0,0 +1,35 @@
+Content from sites such as YouTube can be embedded into a web page. Maybe
+you want to do this. But you'll find that the [[plugins/htmlscrubber]]
+doesn't let you. It blocks the tags used to embed such content, because
+they can be abused in many evil ways.
+
+Some plugins have been written to try to work around this problem, by
+whitelisting the html needed to embed things from a few sites like Google
+calendar, videos, and YouTube. The problem with these plugins is that they
+have to be kept up to date to add new sites, and follow changes to the html
+such sites use for embedding.
+
+(Digression: The real problem with the plugins is that they hide the
+underlying trust relationship. If you decide to embed html from a site,
+you'd better trust that site. And if ikiwiki lets you enter such html, it
+needs to trust you.)
+
+The [[plugins/htmlscrubber]] offers a different way around this problem.
+You can configure it to skip scrubbing certian pages, so that content from
+elsewhere can be embedded on those pages. Then use [[plugins/lockedit]]
+to limit who can edit those unscrubbed pages.
+
+For example, suppose your blog is all under `blog/*`, and you want
+only yourself to be able to post there, and you'd like to be able to embed
+youtube videos etc in your blog. Other users can edit some pages in the
+wiki (Discussion pages, say), but not your blog posts. Then you could configure
+ikiwiki as follows:
+
+	htmlscrubber_skip => 'blog/* and !*/Discussion',
+	locked_pages => '!*/Discussion',
+
+More simply, you might want to allow yourself to embed content anywhere
+on the wiki, but scrub content written on Discussion pages:
+	
+	htmlscrubber_skip => '!*/Discussion',
+	locked_pages => '!*/Discussion',

doc/tips/upgrade_to_3.0.mdwn

@@ -82,7 +82,14 @@ Otherwise, follow this procedure to upgrade a wiki using the aggregate plugin:
    `ikiwiki-transition aggregateinternal your.setup`,
 3. Refresh the wiki. (`ikiwiki -setup your.setup -refresh`)
 
-## googlecalendar
+## embed / googlecalendar
 
-This plugin has been deprecated for a long time, and is removed in 3.0. If
-your wiki used it, you should enable the [[plugins/embed]] plugin, instead.
+The googlecalendar plugin has been deprecated for a long time, and is
+removed in 3.0.
+
+The embed plugin is also now deprecated, though not yet removed.
+
+If you use either plugin to embed content from google, youtube, etc,
+into your wiki, you should instead configure the [[plugins/htmlscrubber]]
+to skip sanitising some pages, via the `htmlscrubber_skip` setting.
+See [[embedding_content]] for examples.