I know that the middle tap should toggle full screen mode but I didn't find it to be the case. I spent hours testing taps all over the screen to try to figure out which tap did what so I could set preferences. The tap options didn't make any sense without knowing the "zones". I was using the English version and tried to use
this site to teach myself the software.
The issue may have been due to the CE software that was funky on my JE100. Honestly, I didn't try it after I updated the firmware.
I look forward to any addition to reading software, especially ePub so I hope the program you are watching is released soon. CE needs it.