Two short (80cm) can be connected together but you'll have to do some "work". They offer a 80cm rail (pictured below) and a 160cm rail.
I only have 2x 80cm rails which come with a self contained clamping system of their own (visible in the pictures below).
As I understand it the larger 160cm rail comes without this self contained clamping system, but uses more traditional screw clamps instead.
You can see how the clamping and connecting of the indexing rails work in this video (08:55) and (11:10)
And now for some pictures. The rails have a t-track in the bottom. On the short (80cm rails) Theres a threaded rod that runs in that t-track that's used to clamp the rail to a workpiece.
(click image to enlarge)
The way it works is the clamping block (left) can quickly be slided up to the edge of your workpiece and you then turn the round knob (right) to tighten the left block to the workpiece, and thus clamping it.
By removing this threaded rod and clamping mechanism, you can simply connect 2 (or more) rails together with a connector bar. (which looks very similar to what Festool uses to connect their rails by the way.)
(click images to enlarge)
Anyway, once you take the clamping system out and connect 2 rails together, you can then just use the special mafell screw clamp in the t-track (pictured below) to index your rail. On the other end you can just use a simple standard scerw clamp in the t-track.
See 11:10 in the video above.
So in essense you clamp it like any other regular guide rail as with other manufacturers.
(click images to enlarge)
What stops the 'Stop Clamp' from sliding up and down the track?