Notes on MathML and SVG support

doc/users/jasonblevins.mdwn

@@ -5,14 +5,18 @@ which, with some patches and a (currently unreleased) plugin, will
 convert inline LaTeX expressions to MathML.  I'm working towards a
 patchset and instructions for others to do the same.
 
-There is one thing that needs to be decided first: whether or not to
-include [[sanitization|todo/svg]] of MathML in htmlscrubber (and while
-we're at it, why not SVG).
+I've setup a test ikiwiki [here](http://xbeta.org/colab/) where I've
+started keeping a few notes on my progress.  There is an example of
+inline SVG on the homepage (note that the logo scales along with the
+font size).  There are a few example mathematical expressions in the
+[sandbox](http://xbeta.org/colab/sandbox/).  The MathML is generated
+automatically from inline LaTeX expressions using an experimental
+plugin I'm working on.
 
 My (also MathML-enabled) homepage: <http://jblevins.org/> (still using
 Blosxom...maybe one day I'll convert it to ikiwiki...)
 
-Current issues of interest:
+Current ikiwki issues of interest:
 
  * [[bugs/recentchanges_feed_links]]
  * [[bugs/HTML_inlined_into_Atom_not_necessarily_well-formed]]
@@ -20,3 +24,50 @@ Current issues of interest:
  * [[todo/BibTeX]]
  * [[todo/svg]]
  * [[todo/Option_to_make_title_an_h1?]]
+ * [[bugs/SVG_files_not_recognized_as_images]]
+
+## MathML and SVG support
+
+So far, I've made some notes on sanitizing MathML and SVG via
+htmlscrubber on the [[todo/svg]] todo item.
+
+I've also worked out some content-negotiation issues.  First of all,
+one needs to modify the default templates to use the
+XHTML+MathML+SVG doctype (see e.g., this [patch][template-patch]).
+For most browsers, the content type of the pages should be
+`application/xhtml+xml`.  The solution is easy if you want to
+just send `application/xhtml+xml` to everybody:
+just change the content type of `.html` files across the board.
+
+However, if you want to support browsers that don't accept
+`application/xhtml+xml` (and those that will but say they
+don't, such as IE with the MathPlayer plugin), then one
+needs a `mod_rewrite` rule like the following:
+
+    RewriteCond %{HTTP_ACCEPT} application\/xhtml\+xml [OR]
+    RewriteCond %{HTTP_USER_AGENT} (W3C.*Validator|MathPlayer)
+    RewriteRule \.html$ - [T=application/xhtml+xml]
+
+This solves the problem of MathML and inline SVG in static pages
+but some additional work is required for dynamically generated
+pages, like page previews, that are generated by `ikiwiki.cgi`.
+We need to allow `ikiwiki.cgi` to set the content type dynamically
+based on the `HTTP_CONTENT_TYPE` environment variable
+(e.g., with the following [patch][cgi-patch]).  Then, the following
+rewrite rules can pass the correct content type to ikiwiki:
+
+    RewriteCond %{HTTP_ACCEPT} application\/xhtml\+xml [OR]
+    RewriteCond %{HTTP_USER_AGENT} (W3C.*Validator|MathPlayer)
+    RewriteRule ikiwiki.cgi$ - [T=application/xhtml+xml]
+
+One final critical issue is that a production-ready setup needs to
+implement some sort of on-the-fly error handling.  If a user submits
+an invalid LaTeX expression or SVG code (not malicious, just invalid)
+and saves the page, then browsers like Firefox will halt processing of
+the page, preventing any further viewing or editing.  A less than
+optimal solution is to force users to preview the page before saving.
+That way if someone introduces invalid XHTML then they can't save the
+page in the first place (unless they post directly to the right URL).
+
+ [template-patch]: http://xbeta.org/gitweb/?p=xbeta/ikiwiki.git;a=blobdiff;f=templates/page.tmpl;h=380ef699fa72223744eb5c1ee655fb79aa6bce5b;hp=9084ba7e11e92a10528b2ab12c9b73cf7b0f40a7;hb=416d5d1b15b94e604442e4e209a30dee4b77b684;hpb=ececf4fb8766a4ff7eff943b3ef600be81a0df49
+ [cgi-patch]: http://xbeta.org/gitweb/?p=xbeta/ikiwiki.git;a=commitdiff;h=fa538c375250ab08f396634135f7d79fce2a9d36