Bart mentioned that:
The point ON the boundary is by definition the closest you can get. For a closed domain, this point is defined to be the last point inside the domain and for an open domain this point is defined to be the first point that lies outside the domain.
It perfectly works when applying for integers or real numbers but I found a following article in an book. Note the increment is 0.5.
But I still do not understand - when Size > 4, they consider 4.5 an ON point but it does not fit the definition - "first point that lies outside the domain." because 4.5 is IMHO in the domain as it is greater than 4. Not sure what is actually the first point outside the domain if 0.5 is the increment.. What is the catch here?