When anyone in my world does 11 damage or more on a single blow, they wound. This means that the enemy begins to lose hit points every round from bleeding.
For each 11 damage done, the wound is 1hp per round. If, for example, I hit your character for 47 damage, and your character survives, it would suffer 4hp damage per round thereafter - until the character was healed or it bound wounds.
Binding wounds takes three rounds per degree of the wound; so to bind a 4hp wound would take 12 rounds; however, for each 3 rounds spent, the total loss drops one point. So by round four, you'd be bleeding out 3hp per round, by round seven you'd be bleeding out 2hp and so on.
Goodberry, a healing salve, the recently added druid's vintage or any healing spell will close a wound immediately.
Course, this usually means falling out of combat so that healing can be eaten or applied.
The 12 point alternative is simply that it takes that 1 more hit point to wound the character; and that 47 damage wouldn't quite be enough to cause a 4hp wound, because the multiples are counted out in 12s and not 11s.