1).
Second, the endianness of its memory layout is given by the type parameter `O`,
which can be any type which implements [`ByteOrder`]. In particular, this refers
to [`BigEndian`], [`LittleEndian`], [`NativeEndian`], and [`NetworkEndian`].

A `U128` can be constructed using
the [`new`] method, and its contained value can be obtained as a native
`u128` using the [`get`] method, or updated in place with
the [`set`] method. In all cases, if the endianness `O` is not the same as the
endianness of the current platform, an endianness swap will be performed in
order to uphold the invariants that a) the layout of `U128`
has endianness `O` and that, b) the layout of `u128` has
the platform's native endianness.

`U128` implements [`FromBytes`], [`IntoBytes`], and [`Unaligned`],
making it useful for parsing and serialization. See the module documentation for an
example of how it can be used for parsing UDP packets.

[`new`]: crate::byteorder::U128::new
[`get`]: crate::byteorder::U128::get
[`set`]: crate::byteorder::U128::set
[`FromBytes`]: crate::FromBytes
[`IntoBytes`]: crate::IntoBytes
[`Unaligned`]: crate::Unaligned