Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
it is I who, it is they who
These locutions preserve the nominative case pronouns in predicate nominative functions, perhaps in part because the nominative who follows immediately and therefore agrees with the preceding predicate nominative. Such usages are typically found at the upper levels; most Conversational and Informal uses would start out It is me. See AGREEMENT; CASE (1); IT’S ME.
