Major restructuring of extension processors, not yet complete

resources/public/content/Extensible Markup.md

@@ -36,7 +36,7 @@ Data files can be uploaded in the same way as images, by using the **upload a fi
 
 Graphs can now be embedded in a page using the [Mermaid](https://mermaid-js.github.io/mermaid/#/) graph description language. The graph description should start with a line comprising three back-ticks and then the word `mermaid`, and end with a line comprising just three backticks.
 
-Here's an example culled from the Mermaid documentation.
+Here's an example culled from the Mermaid documentation. Edit this page to see the specification.
 
 ### GANTT Chart
 
@@ -58,6 +58,14 @@ gantt
         Add to mermaid                      :1d
 ```
 
+Mermaid graph specifications can also be loaded from URLs. Here's another example; again, edit this page to see how the trick is done.
+
+### Class Diagram
+
+```mermaid
+data/classes.mermaid
+```
+
 ## Writing your own custom formatters
 
 A custom formatter is simply a Clojure function which takes a string and an integer as arguments and produces a string as output. The string is the text the user has typed into their markdown; the integer is simply a number you can use to keep track of which addition to the page this is, in order, for example, to fix up some JavaScript to render it.