Where the question of costs, amounting to 500l., depends upon a principle of law or matter of right, and is not merely in the discretion of the judge, an appeal will lie from a decision thereon to the Privy Council; e.g., where the "matter at issue" is whether a vendor of land is, in respect of costs of an action by the purchaser to obtain accounts as to payments on account of purchase-money—in the position of mortgagee, so as to be entitled to them as of right.