Using layout to have a preview

Hello,

I think it's could be interesting to have an option, that developpers can use, to transform a panel in the layout, to be an html preview.

For example, I want to develop a markdown preview, but I won't use the preview in a browser, so my idea is to be able to have 2 layouts (side by side) and the first one to write the markdown, and the other one to have an html preview of it.

Of course it's just an example, and could be use for more usage...

Thanks in advance,