Builder package:text-show
A Builder is an efficient way to build lazy Text
values. There are several functions for constructing builders, but
only one to inspect them: to extract any data, you have to turn them
into lazy Text values using toLazyText.
Internally, a builder constructs a lazy Text by filling
arrays piece by piece. As each buffer is filled, it is 'popped' off,
to become a new chunk of the resulting lazy Text. All this is
hidden from the user of the Builder.