//tool handler function
RadEditorCommandList["Select Element Property"] = 
//function name is not needed.
function(commandName,editor,oTool)
{
    // RadEditor old version using editor.ShowDialog function
    // RadEditor Ajax version using editor.showExternalDialog function
    editor.ShowDialog(
        "/common/plugins/RadEditorAjax/Select Element Property/DropDownEditorAjax.aspx",
        //this is the parameter that will be passed to the RadWindow
        editor,
        //dimension
        450,450, 
        //function that is executed when the dialog is closed with the return value.
        //see Default.aspx file 
        function(returnValue)
        {
        },
        null,'Select Element Property');
};