Nick
Just had a read up on RROP and interestingly he does not cover the subject of action being re-opened to players for no-limit:
6. Any wager not all-in must be at least the size of the previous bet or raise in that round.
7. In limit play, an all-in wager of less than half a bet does not reopen the betting for any player who has already acted and is in the pot for all previous bets. A player who has not yet acted (or had the betting reopened to him by another player's action), facing an all-in wager of less than half a bet, may fold, call, or complete the wager. An all-in wager of a half a bet or more is treated as a full bet, and a player may fold, call, or make a full raise. (An example of a full raise on a $20 betting round is raising a $15 all-in bet to $35.) Multiple all-in wagers, each of an amount too small to individually qualify as a raise, still act as a raise and reopen the betting if the resulting wager size to a player qualifies as a raise.
I was thinking of something like this that would better clarify the rule but try to still keep it uncluttered:
31. Raises
A raise must be at least the size of the largest previous bet or raise of the current betting round. If a player puts in a raise of 50% or more of the previous bet but less than the minimum raise, he or she must make a full raise. The raise will be exactly the minimum raise allowed (see exception for multiple same-denomination chips Rule 33). In no-limit and pot limit, an all-in wager of less than a full raise does not reopen the betting round to a player who has already acted where no other action has occured.
Let me know what you think
stuart