I have the following Editor declaration:

      <ce:editor ID="Editor" Runat="server"
        AutoConfigure="Full"
        AutoParseClasses="true"
        BorderWidth="0"
        DisableAutoFormatting="false"
        EnableStripScriptTags="false"
        FilesPath="/sitecore/Shell/Editor"
        Focus="false"
        FrameStyle="margin:0"
        Height="100%"
        ShowDecreaseButton="false"
        ShowEnlargeButton="false"
        ThemeType="Office2003"
        Width="100%"
        UseRelativeLinks="true"
        UseSimpleAmpersand="true">
      </ce:editor>

When I try to get a selected text via JScript code:

  if(editselection.rangeCount > 0)
  {
                var r=sel.getRangeAt(0);
                var clonedSelection = r.cloneContents();
                var div = document.createElement('div');
                div.appendChild(clonedSelection);
                r.collapse(true);
                alert(div.innerHTML);
   }
 

I can not get property editselection.rangeCount worked. It looks like this property does not exist. Where I was wrong?
How can I get a selected HTML text and replace it with my own?

I used the example from the forum but it seems does not work: http://www.cutesoft.net/forums/10645/ShowPost.aspx 
As I can see from assembly I get 5.0 version. Thank you in advance.