HABPanel Template Widget code accessible?

I’m in the process of learning my way around OpenHAB in general and right now I’m most interested in trying stuff out in the Template Widget in HABPanel.
I find it a bit difficult and slow to handle the code in the wigets “edit window” so I would like to edit in a traditional editor.
Can I find the code on disk somewhere and edit it instead, or do I have to code in the widget in the browser?