Nesting is a term related to the placement of “things inside of other things”. Three types of elements are involved:

Since items can be placed in transport units and those units can be put within other transport units, some very complex combinations can result (items placed in transport units, which have been put inside of other transport units, etc...). In principle, there is no limit to the number of layers included in this nesting. There is a set of rules associated with the placement of items whenever nesting is involved:

The figure below attempts to illustrate the principle of nesting.