I'm confused about the effect of traits on action cards. A plain reading of the rules does not indicate that they act as limitations. But that can't be entirely true because the rank of spells is listed as a trait. So that's an example of a trait acting as a limitation. But what about traits like "slayer" and "watcher". Can any character acquire cards with those traits, or must it me a character with a matching trait? If it's not such a restriction, what purpose does the trait serve.
Any help in understanding is appreciated.