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Publication 1220 - Specifications for Electronic Filing of Forms 1097, 1098, 1099, 3921, 3922, 5498, and W-2G
Publication 1187 - Specifications for Electronic Filing of Form 1042-S, Foreign Person's U.S. Source Income Subject to Withholding
Publication EFW2 - Specifications for Filing Forms W-2 Electronically
FATCA XML - FATCA XML Schemas and Business Rules for Form 8966
ACA XML - Affordable Care Act (ACA) Information Returns Schemas and Business Rules