In other cases they give you a tax credit, e.g. your taxable income is reduced, and there are weird rules and games you can play.

In this case you simply wouldn't be charged tax for this purpose. You'd be eligible for whatever tax credit you might otherwise, the point is not to change the tax code, the point is to meet a need, if possible outside the government's budgeting powers, and having done so, allow reaping of the reward for it.