Update selector docs.

tools/dom/src/shared_html.dart

Index: tools/dom/src/shared_html.dart
diff --git a/tools/dom/src/shared_html.dart b/tools/dom/src/shared_html.dart
index d4cea056c526480dcf2d2932b18c07c4be61fed3..c44effcaa37d09e80e029cc60c792b340b1df49a 100644
--- a/tools/dom/src/shared_html.dart
+++ b/tools/dom/src/shared_html.dart
@@ -30,5 +30,39 @@ Element query(String relativeSelectors) => document.query(relativeSelectors);
 @Experimental()
 ElementList queryAll(String relativeSelectors) => document.queryAll(relativeSelectors);
 
+/**
+ * Finds the first descendant element of this document that matches the
+ * specified group of selectors.
+ *
+ * Unless your webpage contains multiple documents, the top-level
+ * [querySelector]
+ * method behaves the same as this method, so you should use it instead to
+ * save typing a few characters.
+ *
+ * [selectors] should be a string using CSS selector syntax.
+ *
+ *     var element1 = document.querySelector('.className');
+ *     var element2 = document.querySelector('#id');
+ *
+ * For details about CSS selector syntax, see the
+ * [CSS selector specification](http://www.w3.org/TR/css3-selectors/).
+ */
 Element querySelector(String selectors) => document.querySelector(selectors);
+
+/**
+ * Finds all descendant elements of this document that match the specified
+ * group of selectors.
+ *
+ * Unless your webpage contains multiple documents, the top-level
+ * [querySelectorAll]
+ * method behaves the same as this method, so you should use it instead to
+ * save typing a few characters.
+ *
+ * [selectors] should be a string using CSS selector syntax.
+ *
+ *     var items = document.querySelectorAll('.itemClassName');
+ *
+ * For details about CSS selector syntax, see the
+ * [CSS selector specification](http://www.w3.org/TR/css3-selectors/).
+ */
 ElementList querySelectorAll(String selectors) => document.querySelectorAll(selectors);