docs for new hook

doc/api/hooks_server-side.md

@@ -247,3 +247,19 @@ Things in context:
 
 This hook will allow a plug-in developer to re-write each line when exporting to HTML.
 
+## exportFileName
+Called from src/node/handler/ExportHandler.js 
+
+Things in context:
+
+1. padId
+
+This hook will allow a plug-in developer to modify the file name of an exported pad.  This is useful if you want to export a pad under another name and/or hide the padId under export.  Note that the doctype or file extension cannot be modified for security reasons.
+
+Example:
+
+```
+exports.exportFileName = function(hook, padId){
+  return "newFileName"+padId;
+}
+```