diff --git a/README.md b/README.md
index 4ccb175..9476b96 100644
--- a/README.md
+++ b/README.md
@@ -352,6 +352,7 @@ $(document).ready(function() {
             <code>// position the dialog box in center-top</code><br>
 			<code>// shifted 20 pixels down</code><br>
 			<code>['center', 'top + 20']</code><br><br>
+            <blockquote>Note that when the width of the viewport is less than 768 pixels, any arithmetics will be ignored (so, things like <code>left + 20</code> will be interpreted as just <code>left</code>)</blockquote>
         </td>
     </tr>
     <tr>
diff --git a/dist/zebra_dialog.src.js b/dist/zebra_dialog.src.js
index 0b12771..2bd9046 100644
--- a/dist/zebra_dialog.src.js
+++ b/dist/zebra_dialog.src.js
@@ -247,6 +247,10 @@
                                                             //  ['center', 'top + 20'] would position the dialog box in
                                                             //  center-top, shifted 20 pixels down.
                                                             //
+                                                            //  Note that when the width of the viewport is less than
+                                                            //  768 pixels, any arithmetics will be ignored (so, things
+                                                            //  like "left + 20" will be read as just "left")
+                                                            //
                                                             //  Default is "center" (equivalent with  ['center', 'center']).
 
                 reposition_speed:           500,            //  The duration (in milliseconds) of the animation used to
diff --git a/src/zebra_dialog.src.js b/src/zebra_dialog.src.js
index 0b12771..2bd9046 100644
--- a/src/zebra_dialog.src.js
+++ b/src/zebra_dialog.src.js
@@ -247,6 +247,10 @@
                                                             //  ['center', 'top + 20'] would position the dialog box in
                                                             //  center-top, shifted 20 pixels down.
                                                             //
+                                                            //  Note that when the width of the viewport is less than
+                                                            //  768 pixels, any arithmetics will be ignored (so, things
+                                                            //  like "left + 20" will be read as just "left")
+                                                            //
                                                             //  Default is "center" (equivalent with  ['center', 'center']).
 
                 reposition_speed:           500,            //  The duration (in milliseconds) of the animation used to