Proper fix (and unit tests) for selector escaping issue.

src/dom/selector.js

@@ -170,7 +170,7 @@ var Selector = Class.create({
         if (root !== document) {
           var oldId = root.id, id = $(root).identify();
           // Escape special characters in the ID.
-          id = id.replace(/[\.:]/g, "\\$1");
+          id = id.replace(/([\.:])/g, "\\$1");
           e = "#" + id + " " + e;
         }
 

test/unit/fixtures/selector.html

@@ -53,6 +53,17 @@
       </span>
     </span>
   </div> <!-- #dupContainer -->
+  <div id="dupContainer.withdot:active">
+    <span id="dupL1_dotcolon" class="span_foo span_bar">
+      <span id="dupL2_dotcolon">
+        <span id="dupL3_dotcolon">
+          <span id="dupL4_dotcolon">
+            <span id="dupL5_dotcolon"></span>
+          </span>
+        </span>
+      </span>
+    </span>
+  </div> <!-- #dupContainer.withdot:active -->
 
   <div id="grandfather"> grandfather    
     <div id="father" class="brothers men"> father      

test/unit/selector_test.js

@@ -397,6 +397,14 @@ new Test.Unit.Runner({
     
     this.assertEqual(a, b);
   },
+  testElementDownWithDotAndColon: function() {
+    var a = $('dupL4_dotcolon'); 
+    var b = $('dupContainer.withdot:active').down('#dupL4_dotcolon');    
+    var c = $('dupContainer.withdot:active').select('#dupL4_dotcolon');
+    
+    this.assertEqual(a, b);
+    this.assertEnumEqual([a], c);
+  },
   
   testDescendantSelectorBuggy: function() {
     var el = document.createElement('div');