Rule 12.6, effectively Boolean expressions in assignment?

[rmgalles]

The second sentence in Rule 12.6 says \"Expressions that are effectively Boolean should not be used as operands to operators other than (&&, || and !).\"

This makes sense for most operators, but what about the simple assignment operator?

Code:

bool a;

a = (b == c); /* is this allowed? */

Perhaps a disclaimer \"other than assignment\" could be added?