Document snap_delta modifier mask.

diff --git a/libs/gtkmm2ext/gtkmm2ext/keyboard.h b/libs/gtkmm2ext/gtkmm2ext/keyboard.h
index 25c5154024d933f02f2f6c5f52658532310925f8..3ffa09f036d618a3f82e866c77dff43334e8cc82 100644 (file)
--- a/libs/gtkmm2ext/gtkmm2ext/keyboard.h
+++ b/libs/gtkmm2ext/gtkmm2ext/keyboard.h
@@ -122,7 +122,12 @@ class LIBGTKMM2EXT_API Keyboard : public sigc::trackable, PBD::Stateful
        static ModifierMask snap_modifier () { return ModifierMask (snap_mod); }
 
        static void set_snap_delta_modifier (guint);
-       /** @return Modifier mask to temporarily toggle between relative and absolute grid setting;
+       /** @return Modifier mask to temporarily toggle between relative and absolute grid setting.
+        *  Absolute grid is for aligning objects with the grid lines.
+        *  Relative grid is for maintaining an initial position relative to the grid lines.
+        *  With this modifier:
+        *  - magnetic or normal grid should snap absolutely to the grid lines
+        *  - no grid should become absolute grid.
         */
        static ModifierMask snap_delta_modifier () { return ModifierMask (snap_delta_mod); }