I would think a set of principles laying out the responsibilities and discretion of government in a way that maximises the amount of individual liberty within the rule of law.
That would mean the right to elect and remove a government (and the method of doing so), the right not to be arbitrarily arrested, the right to equality before the law, the right to freedom of the press and broadcasting, freedom of religious and political expression, and a right to privacy.
There are some aspects of the Scottish Government’s proposals that blur these issues. Two are of particular concern.
Firstly, nuclear disarmament is a valid aspiration but a question of acute political controversy. The only way this could be translated into a constitutional matter is for that document to say that Scotland is a “nuclear-free zone” ie it does not have nuclear weapons on its soil and it does not intend to allow nuclear weapons on its soil.
This might create all sorts of difficulties with Nato membership. These would not be insuperable in terms of policy but the matter might be better resolved by negotiation rather than reference to a constitution.
Secondly, the question of “free education”. This can only be a reference to the vexed question of tuition fees.
An independent Scotland in Europe, under existing policies, would need to allow free tuition to all students who live within the European Union with all sorts of implications for university finance.
This is a legitimate matter for political debate but a constitutional commitment to free education is likely to complicate matters.
Those charged with the writing of any such document must be careful to draw the distinction between those matters that relate to fundamental liberties, and those which ought to be considered in the light of changing economic and political trends.