The side rails either slide out the top, or flip out towards the outside.

It's crazy that there is no online instructions (at least that I can find). I mean I can find a faq about having sex with a non-vertebrate, but not a faq on how to use these things. . .

Hmm, well it says "add sheets to front or back of binder" so maybe the sides pop down or out instead of the middle? Is it constructed like this?:
|---|

because maybe then it goes like this:
\ ---|

The sides look to be hinged (there's a piano hinge at the bottom of each), and there is a spring-loaded lever on each side -- they squeeze inward. However, I can't make the hinges budge. Squeezing those levers doesn't seem to have an effect on anything. I know this has got to be obvious, but I CAN'T FIGURE IT OUT!

More info (searched by patent number).

Jesus, got it.

Push *down* on the tabs, and the whole mechanism flips up.

That was much harder than it needed to be.

Good on finding the patent, though. I wouldn't have thought of that! (And I work with crazy binders, too.)