By Alex Stevenson Follow @alex__stevenson
Such is the furore surrounding the monstrous clash of the parliaments that the second-string efforts of the SNP to rig the vote have not received much attention yet.
Let's put aside the main battlegrounds, about the timing of the independence referendum and the question of whether there will be two or three options on the ballot paper. Both could affect the outcome, which is why they are generating such heat between Westminster and Holyrood.
There is a third area in which, if the SNP got their way, they would be able to tweak the likely result in their favour: the franchise. Who gets to vote?
It might seem like an obvious answer - the Scottish - but it's not quite that simple.
The UK government has already made its position very clear. "It would be possible to create new franchise, with different groups of people entitled to vote," its consultation document states sniffily. "However, the UK government's view is that the existing Scottish parliament franchise achieves the right balance of clarity, consistency and transparency, and would be administratively straightforward to deliver."
Nationalists north of the border aren't so sure. The SNP wants to include 16- and 17-year-olds in the vote, but exclude EU residents who are eligible to vote in Scottish parliament elections.
Of course they would argue that EU residents who live in Scotland are not Scottish at all, and therefore shouldn't have a say in the country's future. That seems reasonable. But on the 16- and 17-year-olds, their justification is far more shaky. They merely point to Lib Dem support for votes at 16 and insist that this referendum is as good a place to start as any.
If the mainstream parties have not realised it by now, the SNP are exceptionally canny political operators. They do not play by the normal cosy rules of the Westminster gang. They are as determined as they are devious. Even on something as innocuous as the franchise, neither side will give in without a fight.