Replace error handler discussion with text from

Stephen Turnbull.

pep-0383.txt

@@ -126,15 +126,17 @@ and returning bytes, would be written as::
           # fn is now a str object
           yield fn.encode(fse, "utf8b")
 
-The encode error handler interface presently requires replacement
-Unicode to be provide in lieu of the non-encodable Unicode from the
-source string.  It promptly encodes that replacement Unicode.  In some
-error handlers, such as the utf8 proposed here, it is simpler
-and more efficient for the error handler to provide a pre-encoded
-replacement byte string, rather than forcing it to calculating Unicode
-from which the encoder would create the desired bytes.  In fact, with
-utf8b, there are required byte sequences which cannot be
-generated from replacement Unicode.
+The extension to the encode error handler interface proposed by this
+PEP is necessary to implement the 'utf8b' error handler, because there
+are required byte sequences which cannot be generated from replacement
+Unicode.  However, the encode error handler interface presently
+requires replacement Unicode to be provided in lieu of the
+non-encodable Unicode from the source string.  Then it promptly
+encodes that replacement Unicode.  In some error handlers, such as the
+'utf8b' proposed here, it is also simpler and more efficient for the
+error handler to provide a pre-encoded replacement byte string, rather
+than forcing it to calculating Unicode from which the encoder would
+create the desired bytes.
 
 A few alternative approaches have been proposed: