HOWTO - Work with the selection in the editor

I have tried this code but it gives an error of Selection is not defined.

FCKeditorAPI.GetInstance("FCKeditor").Selection ;

Could please tell me what it could be i have hooked up the function of Alan as well in editors FCKEditorAPI.js.

I have written this code after the editors instance loaded on the page but it does not work on selction and i ma lookin for math tag in the editors text but it returns false;
So what do u say??


alert(editorInstance.Selection);
alert(editorInstance.Selection.GetType());
alert(editorInstance.Selection.GetSelectedElement());
alert(editorInstance.Selection.GetParentElement());
alert(editorInstance.Selection.SelectNode(editorInstance.Selection.GetParentElement()));
alert(editorInstance.Selection.HasAncestorNode("MATH"));

How can you obtain the source code of the given selection? I would like to modify the insertHtmlCode plug-in to load the source code into the textarea in the plugin's popup window.

Thanks,
Matt