Explanation:

Section 499 
Illustration (e) to sixth exception
499. Defamation.
Sixth ExceptionMerits of public performance- It is not defamation to express in good faith any opinion respecting the merits of any performance which its author has submitted to the judgment of the public, or respecting the character of the author so far as his character appears in such performance, and no further.
ExplanationA performance may be substituted to the judgment of the public expressly or by acts on the part of the author which imply such submission to the judgment of the public.
(e) But if A says- "I am not surprised that Z’s book is foolish and indecent, for he is a weak man and a libertine". A is not within this exception, in as much as the opinion which he expresses of Z’s character is an opinion not founded on Z’s book.