PEP 517: Misc changes from discussion (#288)

pep-0517.txt

@@ -222,10 +222,10 @@ Mandatory.
 
 ::
 
-  def build_sdist(sdist_directory, config_settings):
+  def export_sdist(sdist_directory, config_settings):
       ...
 
-Must build an unpacked source distribution in the specified
+Must export an unpacked source distribution into the specified
 ``sdist_directory``.
 
 An unpacked source distribution (sdist) consists of a directory called
@@ -244,15 +244,21 @@ can only build an sdist from a VCS checkout.
       ...
 
 Must copy or create any files needed to build a wheel of this package into
-``build_directory``. For instance, it is expected  that ``pyproject.toml`` will
-exist in the root of this directory after this hook runs. For tools such as
-`setuptools_scm <https://github.com/pypa/setuptools_scm>`_, this may include
+``build_directory``. For instance, ``pyproject.toml`` should
+be copied unmodified into the root of this directory. For tools such
+as `setuptools_scm <https://github.com/pypa/setuptools_scm>`_, this may include
 extracting some information from a version control system.
 The ``build_wheel`` hook will subsequently be run from the ``build_directory``
-populated by this hook.
+populated by this hook. The contents of the resulting wheel should be the same
+whether ``build_wheel`` is invoked in an original source directory, the build
+directory populated by this hook, or an unpacked sdist directory.
 
-Optional. If this hook is not defined, frontends may call ``build_sdist`` and
-extract the resulting tarball to use as a build directory. Backends in which
+Because the wheel will be built from a temporary build directory, ``build_wheel``
+may create intermediate files in the working directory, and does not need to
+take care to clean them up.
+
+Optional. If this hook is not defined, frontends may call ``export_sdist`` and
+use the unpacked sdist as a build directory. Backends in which
 building an sdist has additional requirements should define
 ``prepare_build_files``.