§ 12. It shall be the duty of the legislature, subject to the
provisions of this constitution, to restrict the power of taxation,
assessment, borrowing money, contracting indebtedness, and loaning the
credit of counties, cities, towns and villages, so as to prevent abuses
in taxation and assessments and in contracting of indebtedness by them.
Nothing in this article shall be construed to prevent the legislature
from further restricting the powers herein specified of any county,
city, town, village or school district to contract indebtedness or to
levy taxes on real estate. The legislature shall not, however, restrict
the power to levy taxes on real estate for the payment of interest on or
principal of indebtedness theretofore contracted.