diff --git a/.gitignore b/.gitignore
index e9f61ee9..43fc9822 100644
--- a/.gitignore
+++ b/.gitignore
@@ -43,3 +43,6 @@ ios/marry/main.jsbundle
 # unfinished documents
 #
 cn-doc.md
+
+experimental code
+experimental/
diff --git a/elements/Shape.js b/elements/Shape.js
index e45b6d4e..4446b51a 100644
--- a/elements/Shape.js
+++ b/elements/Shape.js
@@ -13,7 +13,10 @@ import createReactNativeComponentClass from 'react-native/Libraries/ReactNative/
 const CIRCLE = 0;
 
 /**
+ * coord props
  *
+ * algorithm for radius in percentage
+ * radius = Math.sqrt(Math.pow((width*percent), 2) + Math.pow((height*percent), 2)) / Math.sqrt(2);
  */
 const CIRCLE_COORDS = ['cx', 'cy', 'r'];