Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
it
is the third person singular neuter pronoun; both nominative and objective cases have the same form. It is used as a formulaic function word to begin sentences such as It’s raining and It’s time to go. It occasionally causes problems because of vague reference to its antecedent. See IT IS I WHO; IT’S ME; THAT (2).
