How is this constructed?

[Brian Penning]

I like this idea for storage but can't figure how these companion boards/leaves are made.
Thoughts?
TIA
http://www.vtfurnitureworks.com/furniture/dtables/self_store_leaves.htm

[Justin Leiwig]

The ones that I have seen run on a sideways u shaped track. When you pull it out and pull up it goes into the upper track and then when you want to close it, you just reverse the procedure and it rolls down to the bottom of the U shape. You just have to make sure the distance between the centerline of the paths of the U is the same width as the table top.

[Jack Wilson50]

I made one years ago, the center top floats on the frame and the company boards are on two tapered rails the lift the center as you pull them out, then the center drops back down and rest on the tapered rails. I think I got the plans from a Fine Woodworking issue; but it was twenty years ago. We used the table for many years, but finally out grew it.

[Derek Stockley]

I'm fairly certain that the book Tage Frid Teaches Woodworking Volume 3 has detailed drawings for this type of table. I found a copy at my local library some time back while researching for a similar project.

[Paul Williams]

A slightly different way to accomplish the same thing. I have my great grandmother's table. It stores 4 large leaves under the top. They are mounted to the sliding rails with "Z shaped" iron pins. You open the table past the length of the leaf or leaves you want. The leaf pivots up and back on the pins. Then you push the table back together. It does have a rather large skirt to hide the rails and the leaves.

[Michael Panis]

I made one years ago, the center top floats on the frame and the company boards are on two tapered rails the lift the center as you pull them out, then the center drops back down and rest on the tapered rails. I think I got the plans from a Fine Woodworking issue; but it was twenty years ago. We used the table for many years, but finally out grew it.
We have a large 19th century dining room table that works just this way. It's pretty amazing.