Section 6-2.1. Estates in severalty, joint tenancy, tenancy by the entirety and

in common
    Estates  as  to  the  number of persons owning an interest therein are
  classified as follows:
    (1)  In severalty.
    (2)  Joint tenancy.
    (3)  Tenancy in common.
    (4) Only as to real property and, on and after January first, nineteen
  hundred ninety-six, as to the shares of stock of a cooperative apartment
  corporation  allocated  to  an  apartment  or  unit  together  with  the
  appurtenant proprietary lease, tenancy by the entirety.