added some comments and dokus

html/functions.php

@@ -1,10 +1,34 @@
 <?php
 
+/// Send Error To Client
+/** @return error message from server to client
+
+    Function calls exit to terminate.
+
+    Message format is json:
+    @code
+    {
+      success: false,
+      txt:     'error message string';
+    }
+    @endcode */
 function error($txt) {
   echo json_encode(array('success' => false, 'txt' => $txt));
   exit;
 }
 
+/// Send Success To Client
+/** @return success message from server to client
+
+    Function calls exit to terminate.
+
+    Message format is json:
+    @code
+    {
+      success: true,
+      txt:     'success message string';
+    }
+    @endcode */
 function success($txt) {
   echo json_encode(array('success' => true, 'txt' => $txt));
   exit;