The rules for minimum raise amounts are in the TDA rules, and RRoP also references something similar. It is slightly different for Fixed-Limit vs No-Limit, since the bet only has to be 1/2-size to be considered a full bet in Limit.... plus the next bet size in Limit is always twice the previous amount (unlike No-Limit). A bet in No-Limit is only considered 'complete' if it meets the minimum raise amount (or a combination of subsequent raises brings the total to completion).
The rules also stipulate what reopens the action, and for whom. For example:
blinds 250/500
utg calls 500
utg+1 folds
mp1 raises to 1200
mp2 calls 1000 all-in
mp3 raises to 1500 all-in
hijack calls 1500 all-in
cut-off
button
sb
bb
At this point, the cut-off player can fold, call 1500, or raise to at least 2200 (700 is the minimum raise amount, since the mp1 raise was 700 more than the previous bet amount of 500). If the cut-off player does not raise, the button has those same options. Same for the small blind or big blind, if nobody raises before their action -- they can still raise, because they have not yet acted.
If nobody else raises, utg can still re-raise, because they are facing a 1500 bet -- a 1000 raise of their initial 500 call.
However, if nobody else raises, mp1 can only call or fold, since 1500 is not a full raise of their previous 1200 raise amount (a complete bet would be facing 1900 or more). But if somebody had raised to at least 1900, it would open their action. For example, if the button had raised to 1900 all-in, followed by no more raises, then mp1 would be facing a full raise of 700 over their previous bet of 1200, and could re-raise (because even though that 700 total came about in two different actions, it still 'completes' the minimum raise amount). But if they only call, then hijack can only call or fold, since they are facing only a 400 raise over their original 1500 call.
Clear as mud? Basically, the rules exist to protect players who have not yet acted, and to ensure that a player cannot re-raise if has already acted unless facing a full minimum raise amount over his prior bet amount. Just remember those two details and it's easy to work out. And it's a textbook example of why all bets should be kept in front of the respective players until ALL action is complete.