The pivot view may sum fields that are not really summable:
unsigned values (e.g. in the case of refunds)
values in different UOM, currencies (any different units really)
Which causes confusion when these fields are displayed.
We add support for the string and invisible attributes in the pivot view,
so that a field can be given a more informative name or hidden altogether.
opw 1909046
closes odoo/odoo#29144