What is the test for admissible in an action for words spoken or written?

Dairies and Braddock v. Hartley (1848) 3 Ex 200, 154 ER 815, is referred to in the last case. The headnote is: “In an action for words spoken or written, the ordinary sense of those words is to be taken as the meaning of the speaker or writer, unless something be shown to have taken place which may give a peculiar character to the expressions used. In the absence of any such evidence, a witness cannot be asked the question, ‘What did you understand by the words?’ The proper course to be adopted is first to lay the foundation by giving such evidence, and then the question becomes admissible.”