In my understanding, NIW based green card application should be self sponsored, however, on the offivial website of uscis, it says: "USCIS Form I-140 Petition for Alien Worker is required. Your employer must file a USCIS Form I-140 (Petition for Alien Worker) at the USCIS Regional Service Center that serves the area where you will work." This makes me quite confusing, should the applicator or his/her employer file I-140 for a NIW based application? Who should be the sponsor? Thanks a lot.