Extendable HTML elements

Having extendable nodes is great, let's also have extendable HTML elements.
Actually i'm setting `path` inside my JSON source so when a node selected i know path to file and do various operations.

But what when we need to read that data on another events, e.g. on context menu?

I guess lets add that data to the HTML as well.
And to avoid clutter, let's add only attrs starting with `data-`.
Makes sense?