--- a/www/HACKING.rst	Fri May 08 23:19:32 2020 +0300
+++ b/www/HACKING.rst	Fri May 08 23:19:59 2020 +0300
@@ -205,6 +205,20 @@
 For cut-off point I chose ``beseech`` word. All less frequent words receive
 ``rare`` marker.
 
+gaphrase & gadialog file formats
+================================
+
+``gaphrase`` & ``gadialog`` files keeps data for generating one side Anki cards.
+
+Both use same numbering schema that allows to merge updated articles with
+original without losing learning progress:
+
+* First line of file starts with ``## NUM`` - to keep track latest used number.
+* Aticles are separated by number line with format ``# NUM``.
+
+``gadialog`` additionally maintains dialog, each part is marked by line starting
+with ``- TEXT``.
+
 C5 dictionary source file format
 ================================