added FW_Flash_Messages

helpers/php.rst

@@ -559,6 +559,8 @@ Database
 
 * ``fw_set_db_extension_data($extension_name, $key, $value)`` - extensions uses this function to store private values in the database.
 
+.. _fw-form:
+
 FW_Form
 -------
 
@@ -664,4 +666,41 @@ Run the initialization script:
         });
     });
 
+.. _fw-flash-messages:
+
+FW_Flash_Messages
+-----------------
+
+You can display small messages that will be stored on the user's session for exactly one additional request.
+This is useful when processing a form: you want to redirect and have a special message shown on the next page.
+These types of messages are called "flash" messages.
+
+.. _fw-flash-messages-add:
+
+.. rubric:: Adding a flash message
+
+.. code-block:: php
+
+    FW_Flash_Messages::add(
+        'unique-id',
+        __('Test message', 'fw'),
+        'success' // available types: info, warning, error, success
+    );
+
+.. _fw-flash-messages-display:
+
+.. rubric:: Displaying flash messages
+
+In admin the messages are displayed as `admin notices <https://codex.wordpress.org/Plugin_API/Action_Reference/admin_notices>`__.
+
+In frontend the messages are printed in footer,
+then a javascript tries to find on the page the content container and move the messages in it.
+This position guessing sometimes fails when the page has some special html structure
+and the messages may not be visible or will be displayed in an inappropriate place.
+You can choose a place in your template and display the messages manually:
+
+.. code-block:: php
+
+    <?php if (defined('FW')) { FW_Flash_Messages::_print_frontend(); } ?>
+
 .. include:: /links.rst.inc