EtherCard: How to use `Stash` with `httpServerReply`?

Refering to the EtherCard library:

For simplicity sake I would use Stash to dynamically create a web server response. How do I use Stash together with httpServerReply()? I can't find any example using Google.

I can't find any example using Google.

I'm not surprised. What the heck is Stash?