Bit 00: encrypted file. Bit 01: compression option. Bit 02: compression option. Bit 03: data descriptor. Bit 04: enhanced deflation. Bit 05: compressed patched data. Bit 06: strong encryption. Bit 07-10: unused. Bit 11: language encoding. Bit 12: reserved. Bit 13: mask header values. Bit 14-15: reserved.