OANDOH
When used in addressing persons or things the vocative ‘O’ is printed with a capital and without any point following it; e.g. ‘O mighty Caesar! dost thou lie so low’; ‘O world! thou wast the forest to this hart’; ‘O most bloody sight!’ Similarly, ‘O Lord’, ‘O God’, ‘O sir’. But when not used in the vocative, the spelling should be ‘Oh’, and separatedfrom what follows by a punctuation mark; e.g. ‘Oh, pardon me, thou bleeding piece of earth’; ‘For if you should, oh! what would become of it?’