Fleshed out the paragraph on commit provenance.
diff --git a/ContributingCode.wiki b/ContributingCode.wiki
index e112b2f..9265370 100644
--- a/ContributingCode.wiki
+++ b/ContributingCode.wiki
@@ -70,11 +70,13 @@
=== Provenance ===
-Good changes should not be made "on top of" bad changes. New commits
-should be given [http://code.google.com/p/soc/source/list?num=300 the head of Melange's master branch]
+Because integrating a git commit means integrating every commit from
+which it is descended, good changes should not be made "on top of"
+bad changes. New commits should be given
+[http://code.google.com/p/soc/source/list?num=300 the head of Melange's master branch]
as their parent commit unless some particular complexity germane to
the change being made requires some other commit (or commits) to be
-chosen as parents of the new commit.
+chosen as parent(s) of the new commit.
== Code Reviews ==
@@ -110,4 +112,4 @@
_Copyright 2014 Google Inc._
_This work is licensed under a_
[http://soc.googlecode.com/svn/wiki/html/licenses/cc-by-attribution-2_5.html Creative Commons Attribution 2.5 License].
-[http://creativecommons.org/licenses/by/2.5/ http://soc.googlecode.com/svn/wiki/html/licenses/cc-by-2_5-88x31.png]
+[http://creativecommons.org/licenses/by/2.5/ http://soc.googlecode.com/svn/wiki/html/licenses/cc-by-2_5-88x31.png]
\ No newline at end of file
