The endian enumeration is a very simple enum used to communicate what kind of byte ordering certain parts of the library should use to interpret incoming byte sequences. The C version uses macros and can be found here.
Little endian, in which the least significant byte as the first byte value.
Big endian, in which the most significant byte as the first byte value.
Native endian, which is one of big, little, or some implementation-defined ordering (e.g., middle endian). If it is big or little, then
ZTD_NATIVE_ENDIAN == ZTD_LITTLE_ENDIAN, or
ZTD_NATIVE_ENDIAN == ZTD_BIG_ENDIAN.