First we had it, then we didn't and now it's back again.
Yes I'm talking about dual candidacy.
Here's my quick guide. Unlike at Westminster, there are two ways of getting elected for the assembly.
There are 60 seats up for grabs next year. 40 are via the first past the post system, while the other 20 are via a form of proportional representation to get on the regional list.
It used to be the case that you could stand in both. Then Labour, when it was in power, stopped it, making the argument that it rewarded failure in that someone could be rejected by voters under the first past the post system, only to be elected anyway on the regional list.
Big hitters
The best example of this was Clwyd West in the assembly elections in 2003 when the four main parties fielded four candidates and every single one of them won because the three losers won a seat by also standing on their parties' regional list.
The ban has been reversed since the Conservatives have been back in power at Westminster who argue that it disproportionately discriminates against the smaller parties in Wales.
The result now is that it de-risks any attempt by big-hitters to go for first past the post seats because they can still have the back-up of getting a list seat even if they lose out in the constituency contest.
The unwritten aim is also to maintain the quality of candidates by ensuring that those big hitters who do challenge still remain in the assembly.
That is the background to the row about the confirmation of Leanne Wood's decision to go for a list seat.
Personal battle
Two years ago she announced that she would go for the constituency seat in the Rhondda.
It set up a contest against Labour's cabinet member Leighton Andrews in what will be the most high profile personal battle next year.
Labour says the Plaid leader's decision two years ago was portrayed as a bold and brave move, which has not been reflected in the fact that she's going for the list seat as a back up. Leighton Andrews says she should have the courage of her convictions and only go for the constituency seat. In other words, her decision to go for the list is a cop out.
In response, Leanne Wood has accused Labour of mischief-making, saying that Leighton Andrews himself stood as a dual candidate in 2003.
She also makes the point that dual candidacy applies in Scotland.
Home patch
Labour says none of its candidates in Wales will be allowed to be constituency and list candidates.
The Welsh Conservatives have yet to make that decision.
The obvious question to answer is whether their leader Andrew RT Davies, who like Leanne Wood has only ever been elected on the list system, will feel confident enough to challenge Labour for the Vale of Glamorgan constituency seat.
Now that the dual candidacy ban has been removed, he could do so knowing he could still put his name on the regional list.
It must be a temptation for him to challenge, knowing that the Tories held on to this seat with a comfortable majority in the general election, but he'll also be aware of the risk for any party leader to come second in his or her home patch.
