Updating documentation

Author: tbiethman

README.md

@@ -15,6 +15,7 @@ This is particularly useful when tracking in custom variables in analytics:
         _gaq.push(['_trackEvent', 'Engagement', 'Click', selector]);
     }, false);
 
+Selector uniqueness is determined based on the given element's root node. Elements rendered within Shadow DOM will derive a selector unique within the associated ShadowRoot context. Otherwise, a selector unique within an element's owning document will be derived.
 
 Installation
 ------------
@@ -74,6 +75,11 @@ Eric Clemmons : [@ericclemmons](https://twitter.com/ericclemmons)
 
 Releases
 --------
+
+- v2.1.0
+  
+    - 
+
 - v0.1.0
 
     - Big refactor/rewrite using es6

src/isUnique.js

@@ -1,8 +1,11 @@
 /**
- * Checks if the selector is unique
+ * Checks if the selector is unique. The selector is unique 
+ * if the elements root node (either its owner document, or a shadow root)
+ * has exactly one element matching the selector.
+ * 
  * @param  { Object } element
  * @param  { String } selector
- * @return { Array }
+ * @return { Boolean }
  */
 export function isUnique( el, selector )
 {