Dont's can be as important as Do's in UX
While design frameworks should focus on describing positive practices and principles (do's), it's important to provide guidance on avoiding common pitfalls, antipatterns, and errors.
Some best practices are simply easier to articulate in the negative than in the positive. For example, which of these is easier to understand?
- Do ensure that content doesn't move when the user may be reading it. Also, do ensure that content that is supposed to be equal in important is shown simultaneously onscreen (i.e. so that there is no inadvertent bias towards visible vs hidden elements).
- Don't using carousels.
Following the positive guidance (#1) should avoid the use of carousels. But that requires a lot of thinking and a very clear understanding of abstract guidelines on the part of the designer, who has to figure out how to apply the guidelines to a particular widget.
Since carousels are a popular, concrete element, it's very helpful to cover the antipattern specifically as a "don't". The two aren't mutually exclusive: for example, you can articulate a positive principle and also point out common antipatterns to avoid.
This principle is not unique to UX. Since you are discussing this with a developer, it may be helpful to point out that most development guidelines also use a combination of do's and don'ts. For example, the zen of python contains the following don'ts:
Errors should never pass silently.
In the face of ambiguity, refuse the temptation to guess.
...and the Android design principles contain these negatives:
Never lose my stuff
Don't interrupt me unless it's important