I was planning to build an e-ink display when I came across the Xteink X3 online. Somewhere in the fine print, it said the thing was fully programmable. I was sold. When it arrived, I liked how flat it was. It felt solid in my hand. I started adding things to the CrossPoint firmware: a different boot animation, dice I could roll by shaking the reader, a LinkedIn QR code for SF networking events. But getting stuff onto it was tedious. I had to join its hotspot and open a little upload website in my browser. Yuck. While looking for a nicer way to send things to it, a thought struck me. If it looks like paper, it should act like paper. I should be able to print on it. What makes a printer a printer? I wanted to open something on my MacBook, press Print, and pick the Xteink. That meant finding out what my computer expected to find at the other end. I ended up in the Internet Printing Protocol , or IPP. It lets a computer ask a printer what it supports, submit a document, and ask what happened to the job.…