The editor brings you a nice tool that helps you debug your code when customizing it to your needs through plugins or direct changes in the source code. You can enable debugging on it and a debug window will popup with your debugging messages.
To enable it just set the following key in the fckconfig.js file or in your custom Configuration File:
FCKConfig.Debug = true ;
Then, in your code, to show messages in the debug window, you can use the FCKDebug object. It has a single method called "Output" that sends messages to the debug window. This is its syntax:
FCKDebug.Output( message, color, noParse );
Debug Output Object
FCKDebug.OutputObject( anyObject, color );