For a range surrounding a node, set selection index to 0.

chrome/browser/resources/chromeos/chromevox/cvox2/background/cursors_test.extjs

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Include test fixture.
 GEN_INCLUDE(['../../testing/chromevox_next_e2e_test_base.js']);
 
 /**
  * Test fixture for cvox2.cursors.
  * @constructor
@@ skipping 351 matching lines @@
   });
 });
 
 TEST_F('CursorsTest', 'MultiLineOffsetSelection', function() {
   this.runWithLoadedTree(this.multiInlineDoc, function(root) {
     var secondLine = root.firstChild.firstChild.firstChild.nextSibling;
     assertEquals('inlineTextBox', secondLine.role);
     assertEquals('diff ', secondLine.name);
 
     var secondLineCursor = new cursors.Cursor(secondLine, -1);
-    assertEquals(-1, secondLineCursor.selectionIndex_);
+    assertEquals(0, secondLineCursor.selectionIndex_);
     secondLineCursor = new cursors.Cursor(secondLine, 0);
     secondLineCursor.index = 0;
     assertEquals(6, secondLineCursor.selectionIndex_);
   });
 });