This is US centric, it's mentioned on the first page, along with the notes and links.
Reinvesting is a minority, edge case. I can't think of a single VC company in the Bay area that can have founders reinvest shares and not cause issues raising.
"...reinvest shares." I don't understand this. I'm guessing it's my lack of knowledge.
I'd expect "reinvest" to mean "supply more capital to obtain more shares" in an attempt to maintain ownership percentage. The founder would have to already be rather wealthy, or be savvy enough to negotiate some other way to maintain their ownership.
You can borrow against your shares if you have a good relationship with the bank. That will allow you to be wealthy enough to buy some shares in the round. Not enough that you won't get diluted, but not as much as being broke. And of course, you have to pay back the loan.
