In ?property > Description it is stated:

A property can be:
...
(2) most types (this includes constant values, for example, 0)

E.g. I can do:

assume(x,1):
about(x);

Originally x, renamed x~:
  is assumed to be: 1

is(x,1);
                                    true

But, I am missing a useful example for such a property.

Besides, I find these properties confusing as 0 and 1 have parent properties entries in the property lattice, but not 2:

`property/ParentTable`[0];
                     {composite, RealRange(0, infinity)}
`property/ParentTable`[1];
                      {integer, RealRange(1, infinity)}
`property/ParentTable`[2];
                           property/ParentTable[2]