[css-grid] Implicit Named Areas

I find the chapter on Implicit Named Areas:
https://drafts.csswg.org/css-grid/#implicit-named-areas
lacking in details on when and how such an implicit area is created.

For example, is an implicit named area A created in any of the
following cases? (assume 'grid-template-rows:40px' for now)

1: grid-template-columns: [A-start] 40px [] 40px;

2: grid-template-columns: [A-end] 40px [] 40px;

3: grid-template-columns: 40px [A-end] 40px;

4: grid-template-columns: [A-end] 40px [A-start] 40px;

5: grid-template-columns: 40px [] 40px [A-start];

6: grid-template-columns: 40px [A-start] 40px;

7: grid-template-columns: [A-start] 40px [A-end] 40px [A-start] 40px;

8: grid-template-columns: [A-start] 40px [A-start] 40px [A-end] 40px;

9: grid-template-columns: [A-start] 40px [A-end] 40px [A-end];

10: grid-template-columns: [A-end A-start] 40px [] 40px;

11: grid-template-columns: 40px [A-end A-start] 40px;

12: grid-template-columns: 40px [A-start A-end] 40px;

13: grid-template-columns: 40px [] 40px [A-end A-start];

If an area is created, at which lines does it start and end?

Are A-start/A-end lines in both dimensions required for
an implicit named area to be created?  For example, if I use
'grid-template-rows:[A-start] 40px [A-end]' together with the
declarations above, does that change the answers in any way?

The results of these examples in Firefox and Chrome are very
different, so I'd like to know what the exact rules are.

Thanks,
Mats