(4) Trustees may, in their absolute discretion, from time to time, but not more than once in every three years unless the nature of the trust or any special dealings with the trust property make a more frequent exercise of the right reasonable, cause the accounts of the trust property to be examined or audited by an independent accountant, and shall, for that purpose, produce such vouchers and give such information to him or her as he or she may require; and the costs of such examination or audit, including the fee of the auditor, shall be paid out of the capital or income of the trust property, or partly in one way and partly in the other, as the trustees, in their absolute discretion, think fit, but, in default of any direction by the trustees to the contrary in any special case, costs attributable to capital shall be borne by capital and those attributable to income by income.