diff --git a/docs/config.md b/docs/config.md
index 31616db..188f1af 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -6,6 +6,110 @@ Websites evolve over time, and PagePark has features that help you adjust things
 
 All the values described here are added to a config.json file that's stored at the top level of a domain folder. Any time a request comes in for that domain, we read the config.json file in its folder, if there is one, and the values are applied to the request.
 
+#### File extensions
+
+The extension of a file determines how PagePark serves it.
+
+
+
+<table>
+
+<tr>
+
+<td>
+
+.txt
+
+</td>
+
+<td>
+
+The text in the file is returned, the type is text/plain.
+
+</td>
+
+<td>
+
+<a href="http://lucky.wtf/applejoke.txt">applejoke.txt</a>
+
+</td>
+
+</tr>
+
+<tr>
+
+<td>
+
+.xml
+
+</td>
+
+<td>
+
+The text in the file is returned, the type is text/xml.
+
+</td>
+
+<td>
+
+<a href="http://lucky.wtf/davetwitterfeed.xml">davetwitterfeed.xml</a>
+
+</td>
+
+</tr>
+
+<tr>
+
+<td>
+
+.json
+
+</td>
+
+<td>
+
+The text in the file is returned, the type is application/json.
+
+</td>
+
+<td>
+
+<a href="http://lucky.wtf/demo.json">demo.json</a>
+
+</td>
+
+</tr>
+
+<tr>
+
+<td>
+
+.opml
+
+</td>
+
+<td>
+
+The outline is rendered as an expandable outline, the type returned is text/html.
+
+</td>
+
+<td>
+
+<a href="http://lucky.wtf/states.opml">states.opml</a>
+
+</td>
+
+</tr>
+
+</table>
+
+
+
+Any page can be written in JavaScript.
+
+PagePark runs the script, and then returns the value it returns, which usually is HTML text.
+
 #### flProcessScriptFiles
 
 If you set this value false, none of the JavaScript files in the domain folder will be processed. They will be served as text, with the source code in the file. 
@@ -16,7 +120,7 @@ Example:
 
 <pre>{
 
-        "flProcessScriptFiles": false
+   "flProcessScriptFiles": false
 
-        }</pre>
+   }</pre>