Never mind: i found it!!
Edit->Disable or Edit->Enable (command /)
Once upon a time I used closing lines of script steps between
If [1 = 0]
and this might still have a sense, because when you have disabled script steps and only Filemaker Pro available, no Advanced, there's no way to enable them.
If you are using FM14 you can also select the lines you want to disable and press CTRL/CMD "/". (Command slash)