SYSML17 — Lower and Upper Explained

I believe the reason Lower and Upper were added into the standard was to allow for multiplicities that did not follow the multiplicity rules of the standard... I have an example... and I think an example should be in the standard to clarify this mystifying need for lower and upper... because it is not clear really why they are needed...

suppose I have the following
part1[3..4]
part2[3..7]
part3[4..6]

and I want to bind a BoundReferece x to part1.part2.part3 in block y... now I can take several approaches...
1. <<boundReference>> x:Part3 [*[ - this removes the double maintenance problem when multiplicities of the paths change does not restrict anything
2. <<boundReference>> x:Part3 [36..168] - this mimics the multiplicities of the path, so really no restriction
3. <<boundReference>> x:Part3 [2..10] - this restricts the number of part3s that there can be at the end of that path

option 3 could have also been specified as
<<boundReference>> x:Part3 [*]

now block z specializes block x and I have another property a such that
<<endPathMultiplicity>> a:Part3[*[

but this only works if x has multiplicity * otherwise
<<endPathMultiplicity>> a:Part3 [5..20[

if x is <<boundReference>> x:Part3 [2..10] does not work
because 5..20 is not a restriction of 2..10

This is why lower and upper can be different (but constrained by) the multiplicity