Question: Code of the Clans is a field guide in a novel series written by a group of authors that collectively use what pseudonym? 
Sentence (from "Warriors (novel series)"): Warriors is a series of novels published by HarperCollins; it is written by authors Kate Cary, Cherith Baldry, Tui Sutherland, with the plot developed by editor Victoria Holmes, who collectively use the pseudonym Erin Hunter.
Relevant evidence: Yes