Residential Panels Mounted Horizontally

I have just had a query from an old friend.
She has put her home up for sale and the realtor has told her that her horizontal breaker panel is a violation of rule 240.81 and must be changed.
This is in Canada and we do not have a rule 240.81 in the Canadian Electrical Code.
Horizontal panels are common here.
I can not find any rule prohibiting horizontal panels.
Am I missing something?
Yes, her house is in Canada.

I found this:

I don’t know if it helps or not.

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Thanks Scott.
My WAG on the matter;
Originally, about a century ago, houses were wired with open wiring and used open knife switches to switch lights.
The very first code stated that knife switches must be mounted so that gravity would tend to open them if installed vertically.
That rule still applies to knife switches with some qualifications.
In Canada, that rule does not apply to circuit breakers, but apparently it has been morphed over to cover breakers as well under the NEC.
Trying to find a rule that specifically allows horizontal panels in Canada is somewhat like trying to prove a negative.
ps; I started wiring houses in 1956 and knife switches had been phased out by then.
I have only seen them in very old text books.

If you put the panel on its side, the electricity will run out!

and the water won’t, maybe?

The heavy water will. The firewater won’t…