+=============
+Functionality
+=============
+
+The module functionality includes the following user actions:
+
+* "File" menu:
+
+ - "Load text file" : reads and loads the contents of text file to the
+ data model; the previous contents of data model
+ is erased.
+
+ - "Save text file" : dumps the contents of the data model to the text
+ file.
+
+* "LIGHT" menu:
+
+ - "Edit selected line" : allows user to edit the selected text line.
+
+ - "Insert new text line" : inserts the new text line entered by the user before
+ the selected one; if there is no selection, new line
+ is added to the end of the data tree.
+
+ - "Remove line" : removes the selected line.
+
+ - "Clear all" : clears all the contents of the data model.