Html Ajax Control Toolkit, AjaxControlToolkit.ExtenderControlBase ( ) AjaxControlToolkit.BehaviorBase ( ).
, $find javascript , AjaxControlToolkit.ScriptControlBase ( ) Sys.UI.Control ( ).
, DOM, :
<script type="text/javascript">
var editorControl = $get("<%=editor.ClientID%>").control;
editorContorl.set_content("Sample Content");
var content = editorContorl.get_content();
</script>