Clarification on substrings/array sections needed

Help
1

I’d be grateful for comments on my understanding the standard definitions regarding substrings and array sections.

We have following defs in the F2018 standard:

R908 substring is parent-string ( substring-range )
R909 parent-string
is scalar-variable-name
or array-element
[…]

9.5.3 Array elements and array sections
9.5.3.1 Syntax
R917 array-element is data-ref
C924 (R917) Every part-ref shall have rank zero and the last part-ref shall contain a subscript-list.
R918 array-section is data-ref [ ( substring-range ) ]

Am I right to deduce that in

program sc
  character(4) :: stab(5) = (/'abcd','efgh','ijkl','mnop','qrst'/)
  print *, stab(2)(1:1)
    ! is a substring of an array element (outputs 'e')
  print *, stab(1:3)(2:3)
    ! is an array section using a substring-range syntax (outputs 'bcfgjk')
end program sc

I got confused because at first I thought stab(1:3)(2:3) should be a substring, but then I realized that the preceding parent-string stab(1:3) is not an array element.

2

I think that stab(1:3)(2:3) would be considered an array-section of substrings, but I think a follow up question would be, do you have a reason it matters exactly what it’s called? Most of the time it’s just useful to know that it’s legal, but the exact name is not so important.

3

Array-section of substrings is something quite different from a substring of an array-section. The latter could, in principle, be interpreted as (taking the above example as a base)
(stab(1)//stab(2)//stab(3))(2:3) symbolically, of course, taking a substring of an expression is invalid.
Consider following snippet which illustrates the idea.

  character(4) :: stab(5) = (/'abcd','efgh','ijkl','mnop','qrst'/)
  call substr(stab(1:3),12,2,3)
end
subroutine substr(str,size,lower,upper)
  integer, intent(in) :: size,lower,upper
  character(len=size), intent(in) :: str(1)
  print *, str(1)(lower:upper)
end subroutine substr

This is a conforming version with str dummy being an array. A non-conforming but perfectly working version would be using str as a scalar:

character(len=size), intent(in) :: str
print *, str(lower:upper)

So, my reason is that if a student asks what is the difference and why array-section is not valid parent-string of a substring, I need a clear and firmly standard-based answer: stab(1:3)(2:3) is not a substring, no matter how similar to a substring it looks.