An intermediate form used during serialisation, specified as a Monoid. It supports efficient concatenation, and is equivalent to a specialised Endo Tokens type.
It is used for the stage in serialisation where we flatten out the Haskell data structure but it is independent of any specific external binary or text format.
Traditionally, to build any arbitrary Encoding value, you specify larger structures from smaller ones and append the small ones together using mconcat.