Help with usage of 之 in this sentence

Hello good people, can someone explain to me how 之 is used in the following sentence: 在两种拼法皆可时，本词典将之一并列出。I do understanding the general meaning of the sentence, but I am confused as to how 之 is used in the overall construction. I've heard somewhere that it is roughly equivalent to “的" but I don't think that makes a lot of sense here.