The binding legal principles established by this judgment are: (1) Exclusion clauses in professional indemnity insurance policies must be interpreted restrictively and consistently with the commercial purpose of the policy, which is to provide meaningful indemnity against liability for negligent professional advice. (2) An exclusion clause that would render the primary purpose of a professional indemnity policy nugatory or commercially inefficacious will not be given effect unless expressed in clear and unambiguous language. (3) In the context of professional indemnity insurance for financial advisors, 'depreciation' in an investment exclusion clause refers to diminishing value over time resulting from market or investment forces, not to total loss arising from an investment that was fundamentally flawed or incapable of generating appreciable value from inception. (4) In professional indemnity policies for financial advisors, 'representation as to performance' of an investment refers to representations about how well an investment will perform in market conditions, not to representations about the fundamental character or safety of the investment itself. (5) Where an exclusion clause in an insurance policy is ambiguous, it must be construed contra proferentem against the insurer who drafted the policy, and in favor of a construction that gives commercial efficacy to the policy. (6) The onus rests on the insurer to prove that a claim falls within an exclusion clause. (7) Insurance contracts, while subject to general principles of contract interpretation (language, context and purpose in a unitary exercise), require particular attention to their risk-transferring purpose and the need to spell out clearly any specific risks the insurer wishes to exclude.