Both exceptions, the special treatment of // and /^/ by split, are documented in split. Both may deserve to be mentioned in the tutorial quickly for the profit of the unaware. The last remark by ysth about the non-equivalence of /^(?#)/ and /^ /x with // for split purposes is a subtle thing. More subtle if you compare to the fact that / /x, / # /x or even / (?#)/x have the same treatment as // when passed to this function. Looks like a case to be fixed either in the docs or in the code of the Perl interpreter itself (if not barred by compatibility issues).