What is the test for defaming a person who is not a defendant?

Gatley on Libel and Slander, 8th ed. (1981), has the following helpful paragraphs: 281. Words must be published “of the plaintiff.” To succeed in an action of defamation the plaintiff must not only prove that the defendant published the words and they are defamatory: he must also identify himself as the person defamed. “No writing whatsoever is to be esteemed a libel unless it reflects upon some particular person.” “It is an essential element of the cause of action for defamation that the words complained of should be published ‘of the plaintiff.’” There is no cause of action, for instance, if words are defamatory of the plaintiff’s relatives, whether they are alive or dead. 285. Defamation of a class. Where the words complained of reflect on a body or class of persons generally, such as lawyers, clergymen, publicans, or the like, no particular member of the body or class can maintain an action. “If,” said Willes J. in Eastwood v. Holmes, “a man wrote that all lawyers were thieves, no particular lawyer could sue him unless there was something to point to the particular individual.”