This is the bytestring builder that is debuting in bytestring-0.10.4.0, which
should be shipping with GHC 7.8, probably late in 2013. This builder has
several nice simplifications and improvements, and more out-of-box
functionality than the older blaze-builder.
Note that this package detects which version of bytestring you are compiling
against, and if you are compiling against bytestring-0.10.4 or later, will
be an empty package.
This package lets the new interface and implementation be used with most
older compilers without upgrading bytestring, which can be rather
problematic. In conjunction with blaze-builder-0.4 or later, which
offers an implementation of blaze-builder in terms of bytestring-builder,
this should let most people try the new interface and implementation without
causing undue compatibility problems with packages that depend on
GHC 7.6 did debut an almost identical interface and implementation, but with
slightly different module names and organization. Trying to re-export/rename
the builder provided with 7.6 did not turn out to be very practical, because
this interface includes new functions that rely on Builder internals,
which are not exported in 7.6. Furthermore, these module names should be
deprecated in 7.10.