The function of the improvisational sections is that when a student records against such piece then the feedback line under impro sections is gray and the score will not be calculated. It is intended to be applied to the sections in music where improvisation is expected. There can be as many impro sections as you like. However, they can only be erased together.
Here's how to make the impro section:
1. Place the cursor somewhere in the music
2. Press Alt+1 to set the section's beginning and Alt+2 for the end. You can adjust the section by dragging its corners
3. Scroll the page up and click on the 'Edit sections'
4. Click on the 'Set as improvisation' (don't fill the name field nor click the other button)
Done! The improvisational section will appear after a hard refresh (the client will see it right away but your computer may be storing the old information so you need to refresh).