Stating obvious interface facts in requirement

I am working on a requirements document regarding the design of a user interface that someone will build. The structure and contents are clear. No problem with that.

But I need to mention, at the beginning, that the user interface provider must conform to the basic principles stated... (where???) regarding usability, ergonomics, user interface elements, etc. etc. I don't want to specify that the left mouse-click should perform the main contextual action, and the right, the secondary one; that the display should not blink or get flipped for no reason. And all those things.

I know that stating obvious things seems useless, but legally it is not. This sets sometimes a common legal problem with providers. Once, we've bought 100 printers, and in order to turn each one ON, it was required to press the ON button... around ten times! (an electronic misimplementation) The legal battle was almost lost, because the provider argued that turning the printer ON with a single button click was not a requirement. We've won, but just due to a legal arrangement. Since that day, I know that stating what is obvious in any requirement is legally mandatory. If one wants no surprises.

So, I've found that the essential reference for the elementary principles of an interface is the ISO-9241 document, although it seems expensive, huge and over-complicated. I would like to find a simpler, well-known similar reference, to read quickly in a reasonable time, and which serves as a basis for the interaction to the interface builder. Is there some good-reputation standard or known reference slightly equivalent to 9241 to cite?