#PROFONDEUR returns the depth of a field in the tree structure.
Sections at the root return a depth of 0.
Example
-  Section A
- Section B
 -   Section C
- Section D
 
 - Section E
 
 -  Section F
- Section G
 
 
On this tree structure, we get:
- Depth 0: sections A, F
 - Depth 1: sections B, C, E, G
 - Depth 2: section D