Eruvin 98: Bodily Fluids and the Public Domain

3 mishnayot - 1. One reading from a book (a scroll), and the book unfurls because of an incline, he can pull it back, because he's still holding onto it. But what if it rolls off the roof? Isn't it on the ground? That can't be okay. Which leads to the tension between taking care to protect Shabbat by not carrying and taking care to protect the words of the holy the texts. 2. Limiting the details of the next mishnah. What can you put in the public domain? Fragile ones only? What if there are two ledges, like a windowsill? Perhaps an example of the Amoraim bring more strict than the Tannaim... 3. Moving an object at the border between domains, within 4 amot - as long as you don't transfer domains. Including urine and spit. Though let's not take that too far, either.