In other words, attributes should be reserved for lists of tokens, numbers,
simple datatypes, etc.
One nice consequence of this rule is that the need for entity
references (most frequently character entity references) in attribute
values is effectively be removed. (Yes, I've used entity references in
attributes for other things, but not often and never without other
What about a list of tokens that contain chars such as café
Surely we can't rule those out just because English doesn't use them?